Methods and apparatus for oxygenation and/or CO2 removal

ABSTRACT

Described is an apparatus for oxygenation and/or CO2 clearance of a patient, comprising: a flow source or a connection for a flow source for providing a gas flow, a gas flow modulator, a controller to control the gas flow, wherein the controller is operable to: receive input relating to heart activity and/or trachea gas flow of the patient, and control the gas flow modulator to provide a varying gas flow with one or more oscillating components with a frequency or frequencies based on the heart activity and/or trachea flow of the patient.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for oxygenationand/or CO2 removal for a patient, in relation to anaesthesia or moregenerally medical procedures where respiratory function might becompromised.

BACKGROUND TO THE INVENTION

Patients may lose respiratory function during anaesthesia, or sedation,or more generally during certain medical procedures. Prior to a medicalprocedure a patient may be pre-oxygenated by a medical professional toprovide a reservoir of oxygen saturation, and this pre-oxygenation isgenerally carried out with a bag and a face mask. Once under generalanaesthesia, patients must be intubated to ventilate the patient. Insome cases, intubation is completed in 30 to 60 seconds, but in othercases, particularly if the patient's airway is difficult to traverse(for example, due to cancer, severe injury, obesity or spasm of the neckmuscles), intubation will take significantly longer. Whilepre-oxygenation provides a buffer against declines in oxygen saturation,for long intubation procedures, it is necessary to interrupt theintubation process and reapply the face mask to increase the patient'soxygen saturation to adequate levels. The interruption of the intubationprocess may happen several times for difficult intubation processes,which is time consuming and puts the patient at severe health risk.After approximately three attempts at intubation the medical procedurewill be abandoned.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise, reference to such external documents is not to be construedas an admission that such documents, or such sources of information, inany jurisdiction, are prior art, or form part of the common generalknowledge in the art.

SUMMARY OF THE INVENTION

Disclosed is a method of oxygenation and/or CO2 clearance of a patientduring a medical procedure with diminished or risk of diminishedrespiratory drive comprising operating a flow source to deliver anoscillating gas flow to the patient.

It is therefore an object of one or more of the disclosed embodiments tooxygenation and/or CO2 removal for a patient in relation to medicalprocedures (including anaesthesia) and/or to at least provide the publicwith a useful choice.

In the context of this specification “heart activity” is that which maybe depicted as a waveform of its electrical impulses or the pulsatilearterial/venous pressure generated by the beating heart. Furthermore, inthis specification, cardiogenic oscillations refer to the movement ofgas caused by the activity of the heart, and it is understood thatreferences to measuring heart activity include measurements ofcardiogenic oscillations, for example by a flow sensor.

In accordance with at least one of the embodiments disclosed hereinthere is a method of oxygenation and/or CO2 clearance of a patientduring a medical procedure with diminished or risk of diminishedrespiratory drive comprising operating a flow source to deliver anoscillating gas flow to the patient.

In accordance with at least one of the embodiments disclosed herein thepressure and/or flow rate of the gas flow is oscillated.

The gas flow may: oscillates at a frequency between 2 to 200 HZ, has aflow rate amplitude of up to 200 L per min has a pressure amplitude ofup to 50 cmH20, and/or has a waveform shape or one or more of:sinusoidal square triangular, and/or saw tooth.

The oscillation may be delivered and/or determined by patientrespiratory phase.

The gas flow may be oscillated at a frequency(ies) based on or to matchone or more of: patient's heart activity patient's lung's resonantfrequency, random noise, patient's chest wall movement, patient'sdiaphragm muscle, contraction patient's neuron firing, respiratoryactivity CO2 level.

Also disclosed is a method of oxygenation and/or CO2 clearance of apatient during a medical procedure with diminished or risk of diminishedrespiratory drive comprising operating a flow source to deliver aconstant, varying, oscillating, switching flow of gas flow to thepatient.

Also disclosed is an apparatus for oxygenation and/or CO2 clearance of apatient during a medical procedure with diminished or risk of diminishedrespiratory drive, comprising: a flow source, a controller to controlthe flow source to provide: an oscillating gas flow to a patient duringa medical procedure, and/or a constant, varying, oscillating, switchingjet of gas flow to the patient during a medical procedure.

The pressure and/or flow rate of the gas flow may be oscillated.

The gas flow may: oscillates at a frequency between 2 to 200 HZ, has aflow rate amplitude of up to 200 L per min, has a pressure amplitude ofup to 50 cmH20, and/or has a waveform shape or one or more of:sinusoidal, square, triangular, and/or saw tooth.

The oscillation may be delivered and/or determined by patientrespiratory phase.

The gas flow is oscillated at a frequency(ies) based on or to match oneor more of: patient's heart activity, patient's lung's resonantfrequency, random noise, patient's chest wall movement, patient'sdiaphragm muscle contraction, patient's neuron firing.

The gas flow may be delivered by one or more of: a nasal cannula,Endotrachael tube, other anaesthetic equipment.

Further disclosed is a patient interface with nasal prongs with adiameter that is configurable.

The gas flow may be delivered by the patient interface of theconfigurations described herein, wherein the prongs are configured bythe controller.

In accordance with at least one of the embodiments disclosed hereinthere is an apparatus according to the various embodiments ofconfigurations described herein further comprising a connector forconnecting the flow source interchangeably between a patient interfaceand a large bore needle.

In accordance with at least one of the embodiments disclosed hereinthere is a system for providing an oscillatory flow of gases thatmatches the heart beats, comprising: a flow source generator and acontroller to influence the flow or parameters or characteristics of theflow such that, in-use, the gases supplied to a user are substantiallymatched to those of the user's heart beat.

In accordance with at least one of the embodiments disclosed hereinthere is a method of matching a flow of gases to a user's heart beat,comprising: measuring or determining the user's heart beat and adjustingor controlling the flow of gas from a source being supplied to the user.

In accordance with at least one of the embodiments disclosed hereinthere is an apparatus for oxygenation and/or CO2 clearance of a patient,comprising: a flow source or a connection for a flow source forproviding a gas flow, a gas flow modulator, a controller to control thegas flow, wherein the controller is operable to: receive input relatingto heart activity and/or trachea flow of the patient, and control thegas flow modulator to provide a varying gas flow with one or moreoscillating components with a frequency or frequencies based on theheart activity and/or trachea flow of the patient.

The apparatus may: comprise a heart activity sensor or has input forreceiving input from a heart activity sensor, and/or comprises memoryfor storing heart activity information, wherein the controller receivesinput relating to heart activity from the sensor, input and/or memory,and/or comprises a flow sensor or has input for receiving input from aflow sensor.

The apparatus may be an apparatus for providing nasal high flow and/orthe apparatus may comprises or be for use with a high flow nasalcannula.

The varying gas flow may have an oscillating flow rate and thecontroller controls the gas flow modulator to provide the varying gasflow with an oscillating flow rate of: about 375 litres/min to about 0litres/min, or preferably of about 240 litres/min to about 7.5litres/min, or more preferably of about 120 litres/min to about 15litres/min.

The oscillating flow rate may comprise a base flow rate component,wherein the base flow rate is about 375 litres/min to 0 litres/min, orabout 150 litres/min to about 0 litres/min, or is preferably about 120litres/min to about 15 litres/min, or is more preferably about 90litres/min to about 30 litres/min.

The apparatus may be for use on persons greater than about 30 kg.

The oscillating flow rate may comprise a base flow rate component,wherein the base flow rate is about 0.5 litres/min to about 25litres/min.

The oscillating flow rate comprises a base flow rate component, whereinthe base flow rate is in the range of 0.4 litres/min per patientkilogram to 0.8 litres/min per patient kilogram.

The apparatus may be for use on persons within about 0.3 to 30kilograms.

The oscillating flow rate may comprise a base flow rate component,wherein the base flow rate is about 8 litres/min for person under about2 kilograms.

The gas flow modulator may be a flow generator and the flow sourcecomprises the flow generator, the controller being operable to controlthe flow generator to provide an oscillating gas flow.

The gas flow modulator may be a valve after the flow source, thecontroller being operable to control the valve to provide an oscillatinggas flow.

The controller may be operable to control the gas flow modulator toprovide a varying gas flow with one or more oscillating components witha frequency and/or phase based on the heart activity.

The relative phase may be either a) in phase with the heart activity, b)in anti-phase with the heart activity, or c) is an arbitrary phase.

The heart activity may have one or more frequencies, and the controlleris operable to control the gas flow modulator to provide an oscillatinggas flow with one or more oscillating components with a frequency orfrequencies different to those of the heart activity.

The heart activity may have one or more frequencies, and the controlleris operable to control the gas flow modulator to provide an oscillatinggas flow with one or more oscillating component with a frequency orfrequencies corresponding to those of the heart activity.

The varying gas flow may have an oscillating flow rate comprising atleast two flow rate components with respective frequencies, wherein afirst flow rate component provides bulk gas flow at a frequencycorresponding to a breath rate of a patient, and a second flow ratecomponent has a different frequency.

The gas flow modulator may be one or more of: an underwater pressurerelease valve, oscillatable diaphragm, in-line linear actuator, flowchopper, aerodynamic or mechanical flutter valve, proportional valve(optionally including a proportional valve with a variable size orifice,variable based on an electrical signal).

The gas flow modulator may be before, in or after the flow source.

The gas flow may have an oxygen fraction of 100%, or 30-40% or 40-50% or60-70% or 80-90% or 90-100%.

The gas flow may have an oxygen fraction of at least about 21% andcomprises one or more of nitrous oxide, nitric oxide and/or helium.

The gas flow may be air.

The apparatus may be adapted to provide gas flow to a patient via apatient interface, either non-sealing or sealing.

The apparatus may be adapted to provide gas flow to a patient via anon-sealing cannula.

The apparatus may comprise a humidifier to humidify the gas flow beforeor after it is oscillated.

The apparatus may additionally comprise one or more sensors formeasuring one or more physiological parameters of a patient, and/or oneor more inputs for receiving a signal from one or more sensors formeasuring physiological parameters of a patient, wherein the one or morephysiological parameters are one or more of: heart activity, oxygensaturation, partial pressure of oxygen in the blood, respiratory rate,partial pressure of CO2 in the blood, exhaled CO2.

The varying gas flow may an oscillating flow rate, and the varying gasflow and/or oscillating flow rate have one or more parameters,comprising one or more of: maximum flow rate, minimum flow rate,frequency period, and the varying gas flow and/or oscillating flow rateparameters are set by the controller based on user input and/orautomatically from measurements of patient physiological functions andpatient physiological parameters.

The controller may be adapted to receive input relating to exhaled CO2and utilise that to control the gas flow.

In accordance with at least one of the embodiments disclosed hereinthere is an apparatus for oxygenation and/or CO2 clearance of a patient,during a medical procedure, comprising: a flow source or a connectionfor a flow source for providing a gas flow, a gas flow modulator, acontroller to control the gas flow by controlling the gas flow modulatorto provide an varying gas flow with one or more frequencies, whereinduring the procedure the patient is apnoeic for at least a portion ofthe procedure and/or the patient is under anaesthesia causing diminishedor risk of diminished respiratory function.

The varying gas flow may have an oscillating flow rate and thecontroller controls the gas flow modulator to provide the varying gasflow with an oscillating flow rate of: about 375 litres/min to about 0litres/min, or preferably of about 240 litres/min to about 7.5litres/min, or more preferably of about 120 litres/min to about 15litres/min, and/or the oscillating flow rate has one or more frequenciesof about 0.1 Hz to about 200 Hz, and preferably about 0.1 Hz to about 3Hz, and more preferably about 0.5 Hz to about 3 Hz.

The oscillating flow rate may comprise a base flow rate component,wherein the base flow rate is about 375 litres/min to 0 litres/min, or150 litres/min to about 0 litres/min, or is preferably about 120litres/min to about 15 litres/min, or is more preferably about 90litres/min to about 30 litres/min.

The oscillating flow rate may comprise a base flow rate component,wherein the base flow rate is about 0.2 litres/min per patient kilogramto about 2.5 litres/min per patient kilogram; and preferably is about0.25 litres/min per patient kilogram to about 1.75 litres/min perpatient kilogram; and more preferably is about 0.3 litres/min perpatient kilogram to about 1.25 litres/min or about 1.5 litres/min perpatient kilogram

The apparatus may be for use on persons greater than about 30 kg.

In accordance with at least one of the embodiments disclosed hereinthere is a method for oxygenation and/or CO2 clearance of a patient,during a medical procedure, comprising: delivering a varying gas flowvia a nasal interface to the patient by varying the gas flow at one ormore frequencies during the procedure while the patient is apnoeic forat least a portion of the procedure and/or the patient is underanaesthesia causing diminished or risk of diminished respiratoryfunction.

The varying gas flow may have an oscillating flow rate of: about 375litres/min to about 0 litres/min, or preferably of about 240 litres/minto about 7.5 litres/min, or more preferably of about 120 litres/min toabout 15 litres/min and/or the oscillating flow rate has one or morefrequencies of about 0.1 Hz to about 200 Hz, and preferably about 0.1 Hzto about 3 Hz, and more preferably about 0.5 Hz to about 3 Hz.

The oscillating flow rate may comprise a base flow rate component,wherein the base flow rate is about 375 litres/min to 0 litres/min, or150 litres/min to about 0 litres/min, or is preferably about 120litres/min to about 15 litres/min, or is more preferably about 90litres/min to about 30 litres/min.

The oscillating flow rate may comprise a base flow rate component,wherein the base flow rate about 0.2 litres/min per patient kilogram toabout 2.5 litres/min per patient kilogram; and preferably is about 0.25litres/min per patient kilogram to about 1.75 litres/min per patientkilogram; and more preferably is about 0.3 litres/min per patientkilogram to about 1.25 litres/min or about 1.5 litres/min per patientkilogram.

The method may be for a patient greater than about 30 kg.

The method may be for providing gas flow prior to the medical procedure.

The gas flow may have a flow rate, wherein a first flow rate providedprior to the medical procedure and a second flow rate is provided duringthe medical procedure, and optionally a third flow rate after themedical procedure.

The second flow rate may be greater than the first flow rate; and/or thethird flow rate may be less than the second flow rate.

The method may have: the first flow rate being about 15 L/min to about90 L/min, or about 20 L/min to about 80 L/min, or about 25 L/min toabout 60 L/min, or about 30 L/min to about 50 L/min, or about 40 L/min,or about 30 L/min; and/or second flow rate being about 20 L/min to about150 L/min, or about 40 L/min to about 120 L/min, or about 50 L/min toabout 100 L/min, or about 60 L/min to about 80 L/min, or about 70 L/min,or about 60 L/min; and/or the third flow rate is less than about 90L/min, or less than about 70 L/min, or less than about 50 L/min, or lessthan about 40 L/min, or less than about 20 L/min, or about 40 L/min, orabout 30 L/min.

The controller may be adapted to receive input relating to exhaled CO2and utilise that to control the gas flow.

The apparatus may be an apparatus for providing nasal high flow and/orthe apparatus comprises or is for use with a high flow nasal cannula.

The method may comprise delivering nasal high flow therapy.

In accordance with at least one of the embodiments disclosed hereinthere is an apparatus for promoting gas exchange with a patient,comprising: a flow source or connection for a flow source for providinga gas flow, a gas flow modulator, a controller to control the gas flow,and wherein the controller is operable to control the gas flow modulatorto provide a varying gas flow with a base gas flow component and atleast one oscillating gas flow component with one or more frequencies ofabout 0.1 Hz to about 3 Hz.

The one or more oscillating gas flow components may have one or morefrequencies of about 0.3 Hz to about 3 Hz.

The varying gas flow may have an oscillating flow rate and thecontroller controls the gas flow modulator to provide the varying gasflow with an oscillating flow rate of: about 375 litres/min to about 0litres/min, or preferably of about 240 litres/min to about 7.5litres/min, or more preferably of about 120 litres/min to about 15litres/min.

The oscillating flow rate may comprise a base gas flow component,wherein the base flow rate is about 375 litres/min to 0 litres/min, orabout 150 litres/min to about 0 litres/min, or is preferably about 120litres/min to about 15 litres/min, or is more preferably about 90litres/min to about 30 litres/min.

The oscillating flow rate may comprise a base gas flow component,wherein the base flow rate about 0.2 litres/min per patient kilogram toabout 2.5 litres/min per patient kilogram; and preferably is about 0.25litres/min per patient kilogram to about 1.75 litres/min per patientkilogram; and more preferably is about 0.3 litres/min per patientkilogram to about 1.25 litres/min or about 1.5 litres/min per patientkilogram.

The oscillating flow rate may comprise at least one oscillating flowrate component, wherein each oscillating flow rate is about 0.05litres/min per patient kilogram to about 0.5 litres/min per patientkilogram; and preferably about 0.12 litres/min per patient kilogram toabout 0.4 litres/min per patient kilogram; and more preferably about0.12 litres/min per patient kilogram to about 0.35 litres/min perpatient kilogram.

The apparatus may be for use on persons greater than about 30 kg.

The oscillating flow rate may comprise a base gas flow component,wherein the base flow rate component is about 0.5 litres/min to about 25litres/min.

The oscillating flow rate may comprise a base gas flow component,wherein the base flow rate component in the range of 0.4 litres/min perpatient kilogram to 0.8 litres/min per patient kilogram.

The oscillating flow rate may comprise at least one oscillating flowrate component, wherein each oscillating flow rate is in the range of0.05 litres/min per patient kilogram to 2 litres/min per patientkilogram; and preferably in the range of 0.1 litres/min per patientkilogram to 1 litres/min per patient kilogram; and more preferably inthe range of 0.2 litres/min per patient kilogram to 0.8 litres/min perpatient kilogram.

The apparatus may be for use on persons within about 0.3 to 30kilograms.

The base gas flow component may be a base flow rate component in therange, wherein the base flow rate is about 8 litres/min for person underabout 2 kilograms.

The oscillating gas flow may have a plurality of oscillating gas flowcomponents at a plurality of frequencies.

The apparatus may have one of more of the frequencies is about 0.1 HZ toabout 3 Hz.

The apparatus may have oscillating gas flow has a period of about 0.3 toabout 10 s.

The controller may be adapted to receive input relating to exhaled CO2and utilise that to control the gas flow.

The apparatus wherein: if the resting heart rate is about 40 to about100 bpm, the oscillation gas flow component has a frequency of about0.67 to about 1.67 Hz, and if the heart rate is about 30 to about 180bpm the oscillation gas flow component has a frequency of about 0.67 toabout 0.5 to about 3 Hz).

The apparatus may be an apparatus for providing nasal high flow and/orthe apparatus may comprises or be for use with a high flow nasal cannula

The term “comprising” as used in this specification means “consisting atleast in part of”. When interpreting each statement in thisspecification that includes the term “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

This invention may also be said broadly to consist in the parts,elements and features referred to or indicated in the specification ofthe application, individually or collectively, and any or allcombinations of any two or more said parts, elements or features, andwhere specific integers are mentioned herein which have knownequivalents in the art to which this invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

It is intended that reference to a range of numbers disclosed herein(for example, 1 to 10) also incorporates reference to all rationalnumbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5,7, 8, 9 and 10) and also any range of rational numbers within that range(for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

“high flow therapy” may refer to the delivery of gases to a patient at aflow rate of between about 5 or 10 LPM and about 100 LPM, or betweenabout 15 LPM and about 95 LPM, or between about 20 LPM and about 90 LPM,or between about 25 LPM and about 85 LPM, or between about 30 LPM andabout 80 LPM, or between about 35 LPM and about 75 LPM, or between about40 LPM and about 70 LPM, or between about 45 LPM and about 65 LPM, orbetween about 50 LPM and about 60 LPM. For example, according to thosevarious embodiments and configurations described herein, a flow rate ofgases supplied or provided to an interface or via a system, such asthrough a flowpath, may comprise, but is not limited to, flows of atleast about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130,140, 150 L/min, or more, and useful ranges may be selected between anyof these values (for example, about 40 to about 80, about 50 to about80, about 60 to about 80, about 70 to about 100 L/min, about 70 to 80L/min).

The invention consists in the foregoing and also envisages constructionsof which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described by way ofexample only and with reference to the drawings, in which:

FIG. 1 illustrates an apparatus/system for oxygenating a patient and/orCO2 removal with high flow gas in relation to anaesthesia.

FIG. 1A schematically illustrates a nasal cannula with adjustablediameter prongs.

FIG. 1B illustrates a large bore needle for flow.

FIG. 1C illustrates a variation of an apparatus/system for oxygenating apatient and/or CO2 removal with high flow gas in relation toanaesthesia.

FIG. 2 illustrates a method for oxygenating a patient with high flow gasin relation to anaesthesia.

FIG. 3 illustrates a method of determining a stage of anaesthesia.

FIG. 4 illustrates airways of a patient.

FIGS. 5A to 5G illustrate a varying gas flow with oscillatingparameters, such as pressure and flow rate.

FIGS. 6 and 7 illustrate an apparatus/system for oxygenating a patientwith high flow gas in relation to anaesthesia and the resultingparameter waveforms according to one example.

FIGS. 8 and 9 illustrate an apparatus/system for oxygenating a patientwith high flow gas in relation to anaesthesia according to alternativeexamples.

FIG. 10 illustrates possible flow rates delivered by apparatus andmethods described.

FIG. 11 shows a cardiogenic waveform for experimental example #1.

FIGS. 12A and 12B show an experimental apparatus.

FIG. 13 shows CO2 concentration in the lung during therapy duringexperimental example #1.

FIGS. 14 and 15A show lung pressure and flow rate during experimentalexample #1.

FIG. 15B shows gas flow in the airway during due to delivery ofoscillating gas flow.

FIG. 16 shows the oscillating flow rate in relation to cardiogenicoscillations.

FIG. 17 shows CO2 clearance in relation to oscillatory component phaseshifts.

FIG. 18 shows an ECG signal, in relation to an oscillating gas flow.

FIGS. 19 and 20 show alternative Gaussian oscillatory flow rate waveformand the related CO2 clearance.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 1. Overview of Embodimentsand Examples

In general terms, apparatus and methods described herein relate to flowtherapy methods and apparatus that assist oxygenation and/or CO2 removalin a respirating patient (respirating referring to either spontaneous orassisted respiration), and preferably during anaesthesia, and/or duringresuscitation, and/or at any medical procedure or other time thatassistance is required. Flow therapy (also termed high flow therapy)relates to apparatus and methods that deliver relatively high flows ofgas to assist a patient respiration.

Some apparatus and methods described herein vary the gas flow togenerate a varying gas flow with gas flow oscillations. This assistswith CO2 removal, and also can assist with oxygenation of a patient. Forexample, parameter(s) of the delivered varying high flow of gas areadjusted to oscillate those parameter(s) to provide a varying gas flow.For example, the pressure and/or flow rate of a delivered high flow ofgas is oscillated. In some embodiments, the oscillations are based on(such as correspond to, or are synchronised with) or are otherwisedetermined using, one or more of: the resonant frequency of patientlungs and/or chest wall, patient cardiogenic pulsations, patientdiaphragm contraction, patient brain activity, patient breathing rate,partial pressures of CO2 or O2, exhaled CO2 or the like and also usingother suitable sensed physiological parameters. Such methods andapparatus can be utilised when the patient is apnoeic or otherwise hasdiminished respiratory function, either during a medical procedure orotherwise. To provide additional efficacy, optionally the patient'soxygenation requirements can be determined and gas flow oscillations canbe adjusted accordingly to improve oxygenation, and/or the patient's CO2can be sensed to assist with determining how to vary the gas flow withgas flow oscillations to remove CO2. As will be described, it has beendetermined that providing gas flow oscillations in a varying high flowgas flow assists with/improves CO2 removal. Apnoea can occur due to, forexample, respiratory depression from anaesthesia (or a variety of othercauses), such that the patient stops breathing.

A continuous supply of oxygen is essential to sustain healthyrespiratory function during medical procedures (such as duringanaesthesia) where respiratory function might be compromised. When thissupply is compromised, hypoxia and/or hypercapnia can occur. Duringmedical procedures such as anaesthesia, the patient is monitored toensure this does not happen. If oxygen supply and/or CO2 removal iscompromised the clinician stops the medical procedure and facilitatesoxygen supply and/or CO2 removal. This can be achieved for example bymanually ventilating the patient through self inflating bag-valve-masks.

In other methods and apparatus described herein, the apparatus and/ormethods can adjust parameter(s) of high flow of gas (e.g. pressureand/or flow rates) in a non-oscillatory manner to be delivered/providedto a patient to assist with oxygenation and/or CO2 removal duringmedical procedures. Patient oxygenation requirements can be determinedto assist.

1.1 Oxygenation and/or CO2 Removal Using Varying Gas Flow

In methods and apparatus described herein, a varying gas flow can beprovided, the varying gas flow being oscillated to create an oscillatinggas flow comprising a base gas flow component and one or moreoscillating gas flow components. The varying gas flow with gas flowoscillations would be useful when a patients' respiratory drive iscompromised or at least reduced, whether this is before, during or aftera medical procedure or in any other situation. The varying gas flow withoscillating components predominantly assists to remove CO2 from arespiring patient. CO2 removal can be useful when a patient is apnoeic,or when a patient has diminished respiratory function, such as whensedated or descending into or coming out of anaesthesia. During theseevents, a patient's respiratory function might not be good enough tosufficiently clear CO2 unassisted. There can be other situations whereCO2 removal assistance is desirable also. As will be described, it hasbeen determined that providing oscillations in a varying gas flowassists with/improves CO2 removal.

Varying the gas flow with oscillating components can also help tooxygenate the patient both directly by assisting the delivery of oxygenand indirectly by removing CO2.

Particular embodiments and examples of apparatus/systems and methods aredescribed for altering the parameters of high gas flow oxygenation. Atleast some of those embodiments can assist CO2 removal from a patient bygas delivery, for example during a medical procedure (such asanaesthesia). Embodiments described are particularly (but not solely)useful for patients that are not spontaneously breathing. When a patientis not spontaneously breathing, their ability to oxygenate and clear CO2can be diminished. Some embodiments relate to apparatus and methods ofoxygenation and/or CO2 removal. In general terms, the embodiments relateto methods and apparatus of utilising a high flow source of gas (such asoxygen and/or other gas mixes) for oxygenating a patient, and/or methodsand apparatus that facilitate removal of CO2.

1.2 Oxygenation and/or CO2 Removal Using High Gas Flow

In a method and apparatus described herein, (high) flow gas (e.g. oxygenor a mix of oxygen and one or more other gases) can be delivered to apatient to reduce the risk of hypoxia. This high flow gas can beprovided during a medical procedure prior to anaesthesia(pre-oxygenation) while the patient is still (spontaneously) breathing,or during anaesthesia (where a patient may not be spontaneouslybreathing and needs assistance), including when the patient might beapnoeic. The use of gas flow provides hands-free oxygenation, unlikecurrent methods, allowing an anaesthesiologist or other clinicians toconcentrate their efforts on the medical procedure itself, without thepatient de-saturating. The gas flow might be provided at a constant flowrate to deliver the “dose” of oxygen required (patient oxygenrequirement) to avoid hypoxia. This dose can also be referred to as therequired “therapy” or “support”. The dose relates to the one or moreparameters of the high flow gas being delivered, and an optimal orrequired dose relates to the high flow gas parameters that provide apatient with their oxygen requirements. For example, the parametersmight be (although are not limited to) one or more of:

-   -   flow rate of gas (such as flow rate of oxygen and including        oscillatory flow)    -   volume of gas delivered    -   pressure of gas    -   composition and/or concentration of gas.        1.3 Determining Oxygenation Requirements

In a method and apparatus described herein, it can be desirable todetermine the oxygen requirements, and adjust (either continuously orperiodically) the gas flow parameters accordingly to ensure oxygenationand/or CO2 removal to the required level. In general terms, thedose/oxygen requirements are determined before anaesthesia and/or during(e.g. thorough continuous or periodic monitoring) anaesthesia, as wellas afterward, including an extubation period; and then the parameters ofthe high gas flow are altered accordingly (manually or automatically) toprovide the required oxygenation to the patient. It should be noted thatreference to “anaesthesia” and its stages throughout this specificationcan refer to actual anaesthesia, and the period prior to anaesthesia(such as the pre-oxygenation stage).

2. First Embodiment of Apparatus/Method for Assisting with CO2 Removaland/or Oxygenation

2.1 Apparatus for Assisting with CO2 Removal and/or Oxygenation UsingVarying Gas Flow

FIG. 1 shows a system/apparatus 10 for delivering a varying gas flowwith oscillations (oscillating gas flow) to a patient to assist with CO2removal, and which can also to assist with oxygenation, in thesituations described above.

The system/apparatus 10 could be an integrated or a separate componentbased arrangement, generally shown in the dotted box 11 in FIG. 1. Insome configurations the system 10 could be a modular arrangement ofcomponents. Hereinafter it will be referred to as system, but thisshould not be considered limiting.

The apparatus comprises a flow source 12 for providing a high flow gassuch as oxygen, or a mix of oxygen and one or more other gases.Alternatively, the apparatus can have a connection for coupling to aflow source. As such, the flow source might be considered to form partof the apparatus 10 or be separate to it, depending on context, or evenpart of the flow source forms part of the apparatus, and part of theflow source fall outside the apparatus.

The flow source could be an in-wall supply of oxygen, a tank of oxygen,a tank of other gas and/or a high flow therapy apparatus with ablower/flow generator 3. FIG. 1 shows a flow source with a flowgenerator 3, with an optional air inlet 6 and optional connection to anO2 source 5 (such as tank or O2 generator) via a shut off valve and/orregulator and/or other gas flow control (all represented as 7), but thisis just one option. In an alternative in FIG. 1C, there is no flowgenerator, but rather the flow source 12 is an in-wall O2 or blendedO2/Air supply, optionally with a flow meter. A shut off valve, regulatorand pressure sensor arrangement 7 is also shown. The description fromhere can refer to either embodiment. The flow source could be one or acombination of a flow generator, O2 source, air source as described. Anyvalves associated with the flow source 12 could be considered part ofthe flow source, or external to it, depending on context. The flowsource is shown as part of the system 10, although in the case of anexternal oxygen tank or in-wall source, it may be considered a separatecomponent, in which case the apparatus has a connection port to connectto such flow source. The flow source 12 provides a (preferably high)flow of gas 13 that can be delivered to a patient 16 via a deliveryconduit 14, and patient interface 15 (such as a (non-sealing) nasalcannula or sealing nasal mask). The flow source could provide a base gasflow rate of between, e.g., 0.5 litres/min and 375 litres/min, or anyrange within that range, or even ranges with higher or lower limits.Details of the ranges and nature of flow rates will be described later.

A humidifier 17 can optionally be provided between the flow source andthe patient to provide humidification of the delivered gas. One or moresensors 18 a, 18 b, 18 c, 18 d, such as flow, oxygen fraction, pressure,humidity, temperature or other sensors can be placed throughout thesystem and/or at, on or near the patient 16. Alternatively, oradditionally, sensors from which such parameters can be derived could beused. In addition, or alternatively, the sensors 18 a-18 d can be one ormore physiological sensors for sensing patient physiological parameterssuch as, heart rate, oxygen saturation, partial pressure of oxygen inthe blood, respiratory rate, partial pressure of CO2 in the blood.Alternatively or additionally, sensors from which such parameters can bederived could be used. Other on patient sensors could comprise EEGsensors, torso bands to detect breathing, and any other suitablesensors. In some configurations the humidifier may be optional or it maybe preferred due to the advantages of humidified gases helping tomaintain the condition of the airways. One or more of the sensors mightform part of the apparatus, or be external thereto, with the apparatushaving inputs for any external sensors.

The output from the sensors is sent to a controller to assist control ofthe apparatus, including among other things, to vary gas flow to providean oscillating gas flow.

As an example, the sensors can comprise a pulse oximeter 18 d on thepatient for determining the oxygen saturation the blood. The pulseoximeter provides an analogue or digital electrical signal for thecontroller 19.

As another example, the partial pressure of oxygen in the blood could besensed by using a transcutaneous oxygen monitor (sensor). The oxygensensor measures the concentration of oxygen and this reading iscorrected for temperature to produce an estimated partial pressure foroxygen in the blood. The instrument electronic system provides ananalogue or digital signal which directly indicates the partial pressureof blood oxygen, and which is connected to the controller 19.

As another example, respiratory rate could be sensed using respiratoryinductance plethysmography (RIP) with an analogue or digital signal thatis connected to the controller 19.

As another example, the partial pressure of CO2 in the blood can besensed using a transcutaneous monitor with an analogue or digital signalthat is connected to the controller 19.

As another example, exhaled CO2 is sensed using an exhaled CO2 sensor.The CO2 partial pressure reading is transmitted to the controller ineither analogue or digital form.

Another example is a heart activity sensor for sensing patient heartactivity. The controller 19 is connected to receive input from the heartactivity sensor (such as a sensor output signal) relating to heartactivity of the patient. This enables the controller to control gas flowbased on the received input from the heart activity sensor.

A controller 19 is provided, which is coupled to the flow source 12,humidifier 17 and sensors 18 a-18 d. It controls these and other aspectsof the apparatus to be described below.

The apparatus also comprises one or more gas flow modulators 59, whichcan be used to modulate (that is, varying, modify, adjust or otherwisecontrol parameters of the gas flow). Each gas flow modulator can beprovided in the flow source (and the flow source itself can be a gasflow modulator), after the flow source and before the humidifier, afterthe humidifier, and/or in any other suitable place in the apparatus tomodulate gas flow path. Examples are shown in FIGS. 1 and 1B, but notall are required, and their position and number can vary based on therequirements of the system. Other examples are described later withreference to FIGS. 6 to 9. Types of gas flow modulators will bedescribed later.

The controller 19 can operate the flow source to provide the deliveredflow of gas. It can also operate the gas flow modulator(s) (includingthe flow source) to control the flow, pressure, volume and/or otherparameters of gas provided by the flow source based on feedback fromsensors, or optionally without feedback (e.g. using default settings).The controller can also control any other suitable parameters of theflow source to meet oxygenation requirements and/or CO2 removal. Thecontroller 19 can also control the humidifier 17 based on feed-back fromthe sensors 18 a-18 d. Using input from the sensors, the controller candetermine oxygenation requirements and control parameters of the flowsource, gas flow modulator(s) and/or humidifier as required. Aninput/output interface 20 (such as a display and/or input device) isprovided. The input device is for receiving information from a user(e.g. clinician or patient) that can be used for determining oxygenationrequirements and/or CO2 detection.

The apparatus can also be operated to determine dose/oxygenationrequirements (hereinafter “oxygen requirements”) of a patient for/inrelation to anaesthesia (that is, the oxygen requirementspre-anaesthesia during a pre-oxygenation phase and/or the oxygenrequirements during anaesthesia—which might include when the patient isapnoeic or when the patient is breathing), as well as after such aprocedure, which may include the extubation period. The system/apparatus10 is also configured to adjust and provide high flow gas to a patientfor the purposes of anaesthesia, and adjust the parameters of the highflow gas (such as pressure, flow rate, volume of gas, gas composition)delivered to the patient as required to meet oxygenation requirements.

2.2 CO2 Removal and/or Oxygenation Using Varying Flow

Use of the apparatus will now be described.

A high flow gas delivered by a high flow therapy method or apparatuscomprises various components with one or more parameters that can beadjusted, including being adjusted to oscillate. Each parameter might beadjusted independently, or in dependence on other parameters. Thisprovides a varying gas flow (varying gas flow parameters). The varyinggas flow (with oscillations) assists CO2 removal and can assistoxygenation.

In one embodiment, the controller 19 is configured to vary the gas flowto create an oscillating gas flow to improve CO2 removal (and optionallyimprove oxygenation). This could be used either during pre-oxygenationor during anaesthesia, or during any other medical procedure where thepatient is apnoeic or otherwise where respiratory function might bediminished. To generate the oscillating gas flow, a parameter orparameters of the delivered gas flow are oscillated, with one or morefrequencies, amplitudes and/or phases. For example, and typically, theflow rate of the gas flow is oscillated with one or more frequencies(including a phase and amplitude), which in turn oscillates the pressuregenerated by the delivered gas flow. However, other parameters could beoscillated—for example the pressure of the gas flow could be oscillated.The oscillating gas flow can comprise one or more oscillatingcomponents, all of different frequencies, amplitude and phase. Theoverall oscillating gas flow can be represented as a (summed) waveform,with a waveform shape comprising the various (summed) oscillatingcomponents. The nature of the varying gas flow is now described withreference to FIGS. 5A to 5D. The varying gas flow has one or moreparameters, including but not limited to, a flow rate (flow rateparameter) and a pressure (pressure parameter). Each varying gas flowparameter (and the gas flow overall) comprises a base component, and oneor more oscillating components which together combine (to create asummed waveform or signal). The varying gas flow overall as a resultmight also oscillate, and oscillation can refer to oscillation of gasflow components, or the overall gas flow. The varying gas flow/gas flowparameters can be represented as one or more waveforms (such as a flowrate waveform and a pressure waveform), with the various componentsmaking up the waveform shape, such as in FIG. 5E. The waveform itselfmay oscillate, and due to the combination of the components will have awaveform shape due to those components. It will be appreciated that thecomponents could be represented or considered as sinusoidal Fouriercomponents, although this is not essential. In this case, the basecomponent would be a fundamental frequency, or DC/bias flow component.

Typically, the apparatus 10 is controlled to generate a varying gas flowwith an oscillating gas flow rate, which results in an oscillating gasflow pressure. The remaining description for FIGS. 5A to 5E will bedescribed in that context. However, this is not essential and it will beappreciated that instead the apparatus could be controlled to oscillatethe gas flow pressure, or other gas flow parameter.

The base flow rate component of a varying gas flow is typically constant(see FIG. 5A), but it could also vary, such as (linear or otherwise)ramping up (See FIG. 5B) or down (see FIG. 5C), or varying in a(relatively slow) oscillatory manner (see FIG. 5D). Oscillation of thebase flow rate, if at all, is generally at a very low frequency. Wherethe base flow rate varies, it can have a maximum and minimum magnitude(amplitude) that it varies between. Likewise, the base pressurecomponent of a varying gas flow is typically constant (See FIG. 5A), butit could also vary, such as (linear or otherwise) ramping up (See FIG.5B) or down (see FIG. 5C), or varying in a (relatively slow) oscillatorymanner (See FIG. 5D). Oscillation of the base pressure, if at all, isgenerally at a very low frequency. Where the base pressure varies, itcan have a maximum and minimum magnitude (amplitude) that it variesbetween. Other gas flow parameters could vary in a similar manner.

The base flow rate component of a varying gas flow can be summedwith/modulated with (e.g. varied, modified, adjusted, or otherwisecontrolled etc.) or otherwise combined with the one or more (relativelyhigh frequency) oscillatory flow rate components each with a frequencyto produce varying gas flow (that may itself oscillate). One oscillatorycomponent summed with the base component is shown in FIGS. 5A to 5D, butmore oscillatory components are possible (such as shown in FIG. 5E anddescribed soon). Each oscillatory flow rate component has a frequencythat is relatively high compared to any slow oscillatory variation ofthe base flow rate. Each oscillatory component has a maximum and minimummagnitude (amplitude). Each oscillatory component also has a phase.Likewise, the base pressure component of a varying gas flow will bemodulated with/summed with or otherwise combined with one or more(relatively high frequency) oscillatory pressure components to producean oscillating varying gas flow. Each oscillatory pressure component hasa frequency that is relatively high compared to any oscillatoryvariation of the base flow rate. Each oscillatory component has amaximum and minimum magnitude (amplitude). Each oscillatory componentalso has a phase.

FIG. 5E shows an example of a general case varying gas flow with a baseflow component (e.g. flow rate or pressure) and plurality of oscillatinggas flow components (e.g. flow rate or pressure), each of which combinetogether to provide a varying gas flow (with a waveform shape) with anoverall period/oscillation.

Generally herein, reference to an oscillatory component or the like willrefer to the high frequency component, not a base component, although itwill be appreciated that all such components can be oscillatory.Hereinafter, references to oscillations will be references tooscillations of pressure and/or flow rate as context allows, but thisshould not be considered limiting and oscillation of other parametersmight be possible. Reference to oscillation can also refer to anoscillation with more than one component and frequency.

As an example, and referring to FIGS. 5E, 5F, the controller 19 varies(by controlling the apparatus) the gas flow flow rate 13 from the flowsource 12 around a base or bias flow rate 50 (bias in the sense of anoffset from zero, equivalent to a DC bias analogy). This provides a(preferably high frequency 51) oscillating gas flow 52 around a(preferably although not necessarily constant) base flow rate 50 thatassists with oxygenation and/or CO2 removal. As an alternative oradditionally, the gas flow base pressure 53 is modified by anoscillating pressure 54 to provide an oscillating gas flow pressure 55.The pressure might be oscillated directly, or indirectly as a result ofoscillating flow rate.

As an example, the frequency of the oscillating component could be 2 to250 Hz, although the frequency could fall outside this range. Morepreferably the frequency is about 100 Hz or less, as this is avoidsdamping issues in the circuit. Where there are multiple oscillatingcomponents, each can be in the range above. Other frequencies arepossible, as described elsewhere herein. For example, the frequencypreferably could be about 0.1 Hz to about 3 Hz.

The frequency or frequencies can be chosen based on a physiologicalparameter. For example, in the case of basing the frequency on heartactivity, frequencies will be around those of heart activity frequencieswhich are generally below 250 Hz. More preferably, the frequency(ies)is/are about 4 Hz or less and more preferably about 2 Hz or less for achild and about 1 Hz or less for an adult. More preferably, thefrequency may be about 0.1 Hz to 3 Hz, or 0.3 Hz to 3 Hz. In eitheroption, the oscillation/variation might not have a single frequency, butmight comprise multiple (including a range of) frequencies (withassociated phases and amplitudes)—see e.g. FIG. 5E. It will beappreciated that the disclosure herein could relate to any sort of flowrate/pressure or other parameter variation/oscillation with one or morefrequencies. Reference in this specification to an oscillation frequencyshould not be considered limiting and should be considered to coveroscillation comprising two or more frequencies, and might also comprisephase/amplitude information.

The varying gas flow flow rate can have the following non-limitingexamples of values. These are made with reference to FIGS. 5A to 5G

Flow rate values for an overall combined/summed waveform will bedescribed first—see, e.g. FIG. 5E. This is one or more oscillatingcomponents summed together with the base component. The overall(oscillating) waveform has a peak flow rate (amplitude), a trough flowrate (amplitude) and an instantaneous flow rate and a period. This gasflow waveform can have an instantaneous flow rate of about 375litres/min to about 0 litres/min, or preferably of about 240 litres/minto about 7.5 litres/min, or more preferably of about 120 litres/min toabout 15 litres/min. The overall waveform can have a peak (maximum) flowrate of about 375 litres/min to about 0.5 litres/min, or preferably ofabout 240 litres/min to about 30 litres/min, or more preferably of about120 litres/min to about 60 litres/min. The overall waveform can have atrough (minimum) flow rate of about 240 litres/min to about 0litres/min, or preferably of about 120 litres/min to 7 about 0.5litres/min, or more preferably of about 60 litres/min to about 15litres/min. The frequency can be about 0.1 Hz to 3 HZ, or 0.3 Hz toabout 3 Hz.

The base component (see FIGS. 5A to 5G), has an instantaneous, maximumand minimum flow rate (amplitude). The base component can have aninstantaneous flow rate of about 375 litres/min to 0 litres/min, or 150litres/min to about 0 litres/min, or preferably of about 120 litres/minto about 15 litres/min, or more preferably of about 90 litres/min toabout 30 litres/min. If the base component varies (e.g. ramps), thecomponent can have a maximum flow rate of about 150 litres/min to about0 litres/min, or preferably of about 120 litres/min to about 15litres/min, or more preferably of about 90 litres/min to about 30litres/min. If the base component varies (e.g. ramps), the component canhave a minimum flow rate of about 150 litres/min to about 0 litres/min,or preferably of about 120 litres/min to about 15 litres/min, or morepreferably of about 90 litres/min to about 30 litres/min. In oneexample, the base component is 30 litres/min to 105 litres/min, butcould be 50 litres/min to 120 litres/min for an adult with BMI>40. Themaximum and minimum flow rates can still fall within the instantaneousflow rate range, and the instantaneous flow rate range can still fallwithin the overall waveform flow rate range.

Each oscillating component has an instantaneous, maximum and minimumflow rate (amplitude), frequency and/or phase. The amplitude of anoscillating component might be defined as a relative amplitude, forexample with reference to the base component, or it might be defined asan absolute amplitude, or both. Each oscillating component can have aninstantaneous flow rate of about 375 litres/min to 0 litres/min, or 150litres/min to about 0 litres/min, or preferably of about 240 litres/minto about 7.5 litres/min, or more preferably of about 120 litres/min toabout 15 litres/min.

The oscillating component can have a maximum flow rate of about 375litres/min to about 0.5 litres/min (or about 270 litres/min to about0.25 litres/min relative to the base component), or preferably of about270 litres/min to about 15 litres/min (or about 120 litres/min to about0.5 litres/min relative to the base component), or more preferably ofabout 150 litres/min to about 30 litres/min (or about 60 litres/min toabout 10 litres/min relative to the base component). The oscillatingcomponent can have a minimum flow rate of about 370 litres/min to about0.5 litres/min (or about 270 litres/min to about 0.25 litres/minrelative to the base component), or preferably of about 240 litres/minto about 15 litres/min (or about 120 litres/min to about 5 litres/minrelative to the base component), or more preferably of about 150litres/min to about 30 litres/min (or about 60 litres/min to about 10litres/min relative to the base component).

The difference between the peak and the trough (peak to peak flow rate)can be a flow rate of about 240 litres/min to 0.5 litres/min, orpreferably 120 litres/min to about 5 litres/min, or more preferably ofabout 60 litres/min to about 10 litres/min, or alternatively about 0 toabout 100 litres/min, or about 40 litres/min to 70 litres/min. Themaximum and minimum flow rates can still fall within the instantaneousflow rate range, and the instantaneous flow rate range can still fallwithin the overall waveform flow rate range. The frequency of anoscillating component can be about 0 to about 200 Hz, or preferablyabout 0.1 Hz to about 20 Hz, or more preferably about 0.5 Hz to about 3Hz, and more preferably about 0.1 Hz to about 3 Hz. The phase can beabout 0 to about 360 degrees or preferably about 0 to about 270 degrees,or more preferably about 0 to 180 degrees.

In more general terms, the instantaneous flow rate of gases at any pointof operation supplied or provided to an interface or via a system, suchas through a flow path, may comprise, but is not limited to, flows of 15litres/min to 150 litres/min and up to 375 litres/min, and optionally atleast about 40, 50, 60, 70, or 80 L/min, or more, and useful ranges maybe selected between any of these values (for example, about 40 to about80, about 50 to about 80, about 60 to about 80, about 70 to about 80L/min, or any other subrange of 15 litres/min to 120 Litres/min, or evenup to 150 litres/min or above).

For example, the base flow range would result in min/max flow of about 8to about 100 L/min and about 30 to about 375 L/min for patients of 40 kgand 150 kg respectively. More preferably, the max/min flow rate is about15 litres/min to 250 litres/min and more preferably 15 litres/min to 70litres/min.

For premature/infants/paediatrics (with body mass in the range of about1 to about 30 kg) the base flow can be set to 0.4-8 L/min/kg with aminimum of about 0.5 L/min and a maximum of about 25 L/min. For patientsunder 2 kg maximum flow is set to 8 L/min. The oscillating flow is setto 0.05-2 L/min/kg with a preferred range of 0.1 L/min/kg and anotherpreferred range of 0.2-0.8 L/min/kg.

The table below illustrates the maximum and minimum flow rates for 40 kgand 150 kg patients respectively (those are somewhat outside the normalmass distribution where the mean for females/males in the US is about75/85 kg respectively, 2004 survey). The flow rates noted are set sothat in the normal ranges, a 150 kg patient can get 30 L/minpre-oxygenation and a very light patient (40 kg) can get ˜50% over thetypical 70 litres/min flow rate. In the case of oscillating flow rates,the minimum oscillating flow for a 150 Kg is 7.5 L/min and the maximumfor a 40 kg patient is 20 L/min. Because pressure is related to flowsquared, the pressure fluctuations are highly dependent on the absolutebase flow rate plus oscillating flow rate or base flow rate minus theoscillating flow rate values

Flow type Min gas Max gas Max Min flow ranges flow range flow for flowfor (L/min/kg) (L/min/kg) 40 kg px 150 kg px Base: example 1 0.2 2.5 10030 Base: example 2 0.25 1.75 70 37.5 Base: example 3 0.3 1.25 50 45Fluctuating: 0.05 0.5 20 7.5 example 1 Fluctuating: 0.12 0.4 16 18example 2 Fluctuating: 0.12 0.35 14 18 example 3

Such relatively high flow rates of gases may assist in providing thesupplied gases into a user's airway, or to different parts of a user'sairway, for example such flow rates may allow for a delivery of suchgases to the upper or lower airway regions, such as shown in FIG. 4.Upper airway region typically includes the nasal cavity, pharynx andlarynx, while the lower airway region typically includes the trachea,primary bronchi and lungs.

By way of non-limiting example, gas flow rates provided by apparatus andmethods described herein could be as also in FIG. 10. All flow ratesherein can be read as about or approximate, and strict compliance withthem is not necessarily required.

When considering the various flow rates described above, it will beappreciated preferably there is not a negative flow rate (that wouldcorrespond to flow going from the patient up towards the apparatus). Itis desired for flow to travel out from the apparatus to the patient. Themaximum amplitude of an oscillatory component allowed is therefore equalto the baseline flow rate. If the amplitude became larger than this, thetrough flow would be less than zero (i.e. this would correspond to flowbeing sucked by the apparatus up from the patient). As such, the flowrates above will be considered in this context and a particular flowrate parameter of a particular component might be influenced by the flowrate parameter of another component.

With a symmetric oscillating component, the maximum peak flow is bydefinition equal to twice the baseline flow. However, under certaincircumstances an asymmetric oscillation could be applied to the flowrate whereby the peak flow could go higher than this, but the troughflow always remain at zero or above.

In more general terms, the controller 19 can be configured to controlthe flow source, generic modulator 59 and/or any other aspect of theapparatus to provide a varying gas flow with: the desired base flow rateand/or pressure (frequency and amplitude) and the desired oscillationcomponent or components (frequency and amplitude) to improve oxygenationand CO2 removal for the patient.

The controller can vary the base gas flow parameter(s) to create theoscillations using any suitable approach. For example, the controllermight directly alter the pressure and/or flow rate by controlling thespeed of the flow source. Alternatively, an external apparatus such asone or more gas flow modulators 59 might be used. The oscillations canbe produced by any suitable mechanical and/or electrical configuration.Any suitable apparatus for oscillation can be used, such as valves(electrical, magnetic or pneumatic, for example), chopper wheels,transducers, pistons, or electronic modulation of the source, forexample. FIG. 1 shows a generic modulator 59 operated by the controllerfor oscillating the gas flow, but this is by way of example and itsposition and nature should not be considered limiting.

The gas flow modulator(s) 59 (see FIG. 1) that creates the pressureoscillations may be positioned anywhere along the length of the system(from the patient end of the interface 15 to the flow source 12) and mayachieve the oscillations 51/54 in a number of ways, such as some of thenon-limiting methods and components listed below. The component 59 maybe removable from the circuit and/or system.

-   -   Electronic valve such as proportional or solenoid valve    -   Rapid variations in blower speed, actioned by the controller.    -   Inline speaker or solenoid actuated diaphragm.    -   Inline linear actuator    -   A rotational or linear flow chopper    -   Any aerodynamic or mechanical flutter valve.    -   Bursts of compressed gas (i.e. air or oxygen) from a compressed        gas source with control valve    -   Motor driving any arrangement of rotational to linear motion    -   Vibrating reeds that create oscillations    -   One way valve/flap that opens at certain pressures, optionally        spring loaded

The addition of flow/pressure oscillations to gas flow as described cando the following.

-   -   Reduce the time averaged flow rate/pressure necessary to achieve        a certain level of oxygenation and CO2 clearance. High flow        rates can be perceived as less comfortable, so any ability to        reduce the flow rate while maintaining the same oxygenation        support is desirable.    -   Increase the total oxygenation and CO2 clearance capacity of        high flow gas delivery    -   Decrease the time required for pre-oxygenation

The oscillation frequency (pressure or flow) of the gas flow could beanywhere from about 2 to about 200 Hz as previously described orotherwise as described elsewhere herein (more preferably, the frequencymay be about 0.1 Hz to 3 Hz, or 0.3 Hz to 3 Hz) and have instantaneouspressure or flow amplitudes of up to 200 L/min and/or 50 cmH2O orotherwise as described elsewhere herein. The waveforms of theoscillations could be any suitable shape. Some examples of waveformshape are:

-   -   Sinusoidal    -   Square    -   Triangular    -   Saw tooth    -   Gaussian    -   Based on physiological waveforms (e.g. blood pressure or        cardiogenic pulsations, cough, sneeze wave patterns etc.)        2.3 Determining Base and Oscillation Component Frequencies,        Amplitudes and/or Phases for Varying Gas Flow

In general terms the, the amplitude, frequency and/or phase of baseand/or oscillation components (including the parameters thereof asstated above) are determined based on default parameters, user input,experimental data and/or physiological parameters. These can be set tooptimise patient response. For example, the frequency and/or amplitudeand/or phase of the base and/or oscillation components of a varying gasflow can be based on one or a combination of various considerations,such as (but not limited to) the following.

Sweeping the frequency and/or amplitude to find an optimum patientresponse.

The respiration rate and phase of the patient.

The resonant frequency of the lungs of the patient.

The resonant frequency of the chest cavity of the patient.

The heart rate (or more generally heart activity) of the patient.

The brain activity of the patient.

Random noise.

Clinician input, for example mean pulmonary artery pressure.

Experimental data or default/predetermined parameters.

Measurement of O2.

Measurement of CO2

Based on the above, the gas flow components have set instantaneousamplitude, frequency, phase, maximum and minimum amplitudes.

For example, oscillation components (that is the various parameters ofcomponents, such as phase, frequency and amplitude) could correspond to(be based on) or be synchronised/matched with one or a number ofdifferent respiratory or other patient parameters. “Correspond” moregenerally means to relate to or be influenced by, but not necessarilymatch (although it could comprise match also).

It has been determined that as CO2 is exhaled through the trachea, aplug of CO2 travels through the trachea and oscillating gas flow assistin clearing this plug from the airways. The apparatus and methodsdescribed above assist to provide CO2 removal and/or oxygenation byproviding for oscillating gas flow. The efficiency of CO2 removal and/oroxygenation can be improved, where the parameters of the oscillationcomponents are based on a physiological parameter, as described above.Oscillations could be chosen to have frequencies and/or phases that arematched to a physiological parameter frequency/phase, or some harmonicor other multiple of that frequency/phase. As another example, theoscillation components could be chosen to have an amplitude(instantaneous, maximum and/or minimum) that is proportional orinversely proportional to the amplitude of the physiological parameter(such as heart activity).

Some of these are described in more detail below, and various otherexamples described demonstrate how a gas flow component (oscillator orbase component) can be based on a physiological parameter.

2.3.1 Heart Activity

Heart activity moves gas flow up and down the trachea of a patient. Theheart has electrical signals that have a fundamental frequency. Theelectrical signals trigger the heart to pump, at that frequency, whichin turn pumps blood with oscillatory pulses at that frequency. Thisinfluences oscillatory contraction and expansion of the lungs at thatfrequency, which in turn can move influence the oscillatory movement ofgas up and down the trachea at that frequency. Heart activity can referto any of these processes and the frequency of heart activity can referto that frequency. While the oscillation at each stage above has thesame frequency, each stage could have a different phase, due to a delaybetween each stage. For example, there could be a phase delay betweenthe oscillating electrical signal occurring and the oscillating gasmovement up and down the trachea.

During the delivery of nasal high flow to a patient, transport to thelungs occurs naturally by Aventilatory Mass Flow. However, the clearanceof CO2 from the lungs must occur against this net flow. Smalloscillations of respiratory flow occurring at the same frequency as theheart activity have been observed during both inspiration andexpiration. The inventors determined that cardiogenic pulsationscombined with turbulence entrained from high pharyngeal flow causelongitudinal mixing of gas within the trachea. The mixing is sufficientto bring CO2 up from the lungs, while also enhancing the transport ofoxygen down the trachea. On the expiratory part of each cardiogeniccycle, a portion of the mixed gas in the trachea is then ejected intothe strongly flushed pharyngeal region. For example, if a gas flow withan oscillating pressure is delivered with an amplitude of pressurefluctuations of 2 cmH2O, then approximately 140-200 ml of gas would bepumped in and then back out of the lungs over each pressure cycle. Theairway dead space is approximately 150 ml, and so in this example about0 ml-40 ml of gas would be cleared from the lungs each cycle. In thissimplified case, clearance would begin to occur when the volume of gaspumped reaches 150 ml per stroke, and this would correspond to apressure variation of 2.14 cmH20 (for the case of low lung compliance inthe example)—1.5 cmH2O (for the case of high lung compliance) in thisexample. It is noted that the airway and lungs can readily withstandpressures of up to 5 cmH2O relative to atmospheric pressure.

As such, the inventors have determined that providing a varying gas flowwith at least one oscillating component of the right frequency, phaseand/or amplitude based on the heart activity frequency can assist theCO2 clearance and/or oxygenation process. For example, if theoscillating component(s) has/have frequency(ies) the same as or near thecardiogenic pulsations (heart activity) creates this effect andfacilitates CO2 removal and/or oxygenation. The varying gas flowprovided can be varied in synchronism with the heart activity, such asby varying the gas flow to have oscillation components withfrequency(ies) matching those of the heart activity. The effect of thisis to move gas up and down the trachea and contributing to CO2 transportout of the lungs and oxygen transport in to them. This effect enhancesthe naturally occurring cardiogenically-induced oscillations of gas upand down the trachea. The net effect of the cardiac-synchronised flowvariations to the flow is to greatly enhance the clearance of CO2achieved by cardiogenesis on its own (typically by a factor of between 3and 10). More generally, the oscillation frequencies do not need to besynchronised with heart activity, but rather correspond to it in someway.

As one example of how a gas flow component can be based on aphysiological parameter; heart activity can be sensed and the frequencyof one or more oscillation components can be made to have a frequencythe same as or similar to the heart activity. Additionally oralternatively, because there is a delay between the heartbeat and thegas flow in the trachea, each oscillation component might have a delay,such as a phase delay, relative to the heart activity waveform, tocompensate for the gas flow delay. Preferably, the gas flow oscillationcomponent is matched as closely as possible to the heart activityfrequency (such as shown in FIG. 18 which shows an ECG signal showingheart activity and an oscillating component with the same or similarfrequency), although some variance is possible, to provide optimum CO2removal and/or oxygenation. The phase is preferably matched, although aphase difference still produces useful effects (such as shown in FIG.11). Also, as mentioned earlier, a phase delay relative to one stage ofheart activity, may help to align with the phase of another stage of theheart activity.

In one exemplary example, the controller 19 can monitor the patient'sheart activity through a sensor (e.g. sensor 18 d) and control thesystem 10 so that gas flow oscillations 52/55 are synchronised/matchedor otherwise correspond with/are based on the patient's heart activity.The controller 19 can be configured to control the flow source 12 toprovide a gas flow that oscillates 52/55 at the same frequency as thatof the (or otherwise based on) patient's heart activity frequency toincrease the mixing of the gases, promoting oxygenation and CO2clearance. The oscillation could be in phase, in anti-phase (or constantrelative phase) or out of phase with the heart rate but preferably in orclose to in phase (or with a phase delay) as previously described. In apreferred example, the frequency of an oscillating component can beabout about 0.1 Hz to about 3 Hz, or preferably 0.5 Hz to about 3 Hz,and, which corresponds to the frequency of typical heart activity.

In one example, the patient's heart activity (including “heart beat” or“heart rate” or any of the heart activity stages as mentioned earlier)could be monitored using sensor 18 d and the output signal could be usedas the input into the controller to determine the frequency of gas flowoscillation 52/55. For example, the heart activity could be monitoredusing sensors e.g. 18 d in one or more of a number of ways. Non limitingexamples follow.

Using a heart rate monitor (heart activity sensor). Flow sensor tomeasure gas flow in the trachea.

Using the plesythmograph signal from a pulse oximeter probe.

Using an ECG signal picked up by electrodes (sensors) attached to theskin (usually the chest) and coupled to a very sensitive amplifier.

In each case, it is the output electrical signal which fluctuates insynchronism with the heart activity that is connected to the controller.

Alternatively or, the user could be prompted to enter the heart activityinformation into the I/O interface 20, from empirical data, previouslyrecorded heart activity, or some other source. In this case, thecontroller 19 receives input relating to heart activity of the patientfrom the I/O—such as from a clinican who takes the patient's pulse.Alternatively or additionally, the heart activity information could bein a memory forming part of or separate to the controller. In this case,the controller 19 receives input relating to heart activity of thepatient from the memory, which could be stored based on e.g. empiricaldata of typical heart activity frequencies and/or typical gas flowoscillation frequencies that prove effective. For example, resting heartrates are typically between 40-100 bpm (0.67-1.67 Hz) but could be inthe range of 30-180 bpm (0.5-3 Hz) under extreme physiology (e.g.

under medical procedures or intense exercise).

Alternatively, the gas flow system 10 could comprise anelectrocardiogram or heart rate monitor or echocardiograph (which couldbe considered heart activity sensors in the system). In this case, thecontroller 19 receives input relating to heart activity of the patientfrom the sensors in the system.

Irrespective of how the heart activity is measured or otherwisedetermined, it can be used by the controller to determine a suitablefrequency(ies) for the oscillation component(s) of the varying gas flow.For example, if the heart rate was measured at 80 beats per minute thehigh flow system could be set to oscillate 52 the flow between 70 L/minand 40 L/min 80 times a minute (1.333 Hz).

In more general terms, the varying gas flow oscillation componentfrequency and phase is based on the gas flow in the trachea. Heartactivity frequency can be used to determine the frequency of gas flow inthe trachea as described above, and therefore the gas flow oscillationcomponent frequency and phase is based on the heart activity frequency.However, another measure could be used for trachea gas flow. For examplea flow sensor could be placed to measure flow rate in the trachea, andthe oscillation component frequency and phase based on the gas flowfrequency is determined from the flow sensor.

Where a sensor is used, there can be continual or periodic feedback ofthe heart rate activity so the frequency and/or of the oscillatingcomponent can be adjusted when it drifts from the desired frequency orphase.

The human body is very adaptable and it is possible the heart wouldsynchronise with oscillatory flow 52/55. Therefore, in an alternative,it is possible the user could enter an oscillatory frequency 51/54 theywished the gas flow to be at and encourage a change in the frequency ofthe heart. In this case, the user could choose to only have the setfrequency or choose to provide some variation to the frequency (e.g. ifthe user set 80 beats per minute the high flow system could cyclebetween ±4 beats per minute around the set point). Variation is thoughtto be beneficial.

The controller 19 can controller the flow source 12 to produce gas flowoscillations in accordance with one of the following.

-   -   The oscillations 51/54 are synchronised so that as the heart        expands, an increase in gas flow is delivered, flushing the CO2        from the airway and displacing it with oxygen from the flow        source. As gas moves up the trachea as a result of the        cardiogenic oscillation the gas flow is reduced to facilitate it        coming up. As the gas goes down the trachea as a result of the        cardiogenic oscillation the gas flow is increased.    -   The oscillations 51/54 are synchronised so that as the heart        expands, a decrease in gas flow is delivered (this could be        positive, zero, or negative), causing a suction effect on the        CO2 drawing it out from the airway and allowing oxygen to        replace it when the flow is increased again.

It will be appreciated that in addition to determining one or moreoscillation/base components for a varying gas flow based on heartactivity, one or more other oscillation/base components of that varyinggas flow could be determined based on other physiological parameters(such as those described next). Any reference throughout thespecification to a varying gas flow with one or more oscillation/basecomponents based on heart activity does not preclude that varying gasflow having one or more other oscillation/base components based on someother parameter, such as a physiological parameter. Multiple oscillatorycomponents, each with frequency, phases and/or amplitudes all determinedbased on multiple different physiological or other parameters could bedetermined and combined to form a varying gas flow for CO2 removaland/or oxygenation. For example, this could be an oscillating gas flowhas a plurality of oscillating gas flow components at a plurality offrequencies. All the examples described herein could be used alone or incombination.

2.3.2 Respiratory Rate

In one example, to assist with determining a suitable oscillationwaveform for the gas flow, the controller can monitor the respiratory(breath) flow of the patient (using one or more of the sensors) todetermine parameters and/or phases of the respiratory flow and thepatient's requirements. For example, the controller 19 can utiliseparameters of the respiratory flow wave (including the phase of breathand/or the transition between inspiration and expiration). Methods andapparatus for respiratory flow wave, meeting (e.g. peak) inspiratorydemand and estimating (e.g. peak) inspiratory demand could be used. Itshould also be noted that the following can utilise switching modes ofoperation between inspiration and expiration. The exact moment ofswitching should not be limited to the exact transition point.

By determining the patient's respiratory flow the controller 19 could beconfigured to operate the flow source 12 and other aspects of the system10 to do one or more of the following.

-   -   Superimpose oscillatory flow 51 (such as in FIG. 5F) on the        respiratory flow.    -   Determine the phase of the breath (inspiratory, expiratory), and        -   only deliver oscillatory flow during a set phase            (inspiratory or expiratory or near the end of expiration),        -   Stop flow during expiration to allow the lung to passively            expire; the “stop” flow being for example 0 L/min or a low            flow (e.g. below 20 L/min), and/or        -   provide oscillatory flow 52 (such as in FIG. 5F) and            intermittently provide negative flow for the expiratory            portion of a breath; the “negative” flow being for example 0            L/min or a negative flow that sucks flow from the patient.

Oscillatory flow could be delivered through the patient interface (e.g.nasal cannula or nasal mask) 15 as done in traditional high flowtherapy. However, in present embodiments where oscillating gas flow52/55 is provided during medical procedures (such as anaesthesia) thereare other possible delivery configurations also, which comprise thefollowing.

-   -   A device (e.g. mask and cannula combination interface 15) could        be used to deliver oscillatory flow 52/55 through the nose and        mouth. The delivered oscillations could be the same or different        for the nose and mouth. They could also be delivered at        different times (e.g. only through the nose, then only through        the mouth)    -   A device (e.g. extended Endotrachael tube) could be used to        deliver different oscillatory flows 52/55 into the left and        right bronchi to maximise the potential to meet the resonant        frequency of each side of the lungs.

2.3.3 Resonant Frequency Lungs

In another example, the controller can control the system so that gasflow oscillations are synchronised/matched or otherwise correspond withthe patient's lung resonant frequency or frequencies. Delivering afrequency that matches the resonant frequency/ies of the lungs as awhole, or a spectrum of frequencies that encompasses the resonantfrequency of the various airways of the lungs encourages mixing,oxygenation and CO2 clearance. The resonant frequency/ies will bedifferent for each patient. The controller 19 is configured via thesensors (e.g. 18 d) and/or other inputs to detect the resonant frequencyof the lungs. This could involve operating the flow source provideoscillating gas flow 52/55 with a sweep of different frequencies over arange of frequencies while a patient is breathing, and monitoring viathe sensor(s) respiratory parameters to provide feedback on whenoxygenation and/or CO2 clearance is greatest. Possible respiratoryparameters can comprise any one or more of the following.

-   -   CO2 (expired, transcutaneous)    -   O2 (expired, transcutaneous, SpO2)    -   Respiratory rate (lower CO2 concentrations lead to reduced        respiratory rates)

Continuous monitoring of the respiratory parameters by the controller 19could be used to ensure the frequency is matched throughout theanaesthetic or other medical procedure period.

In another example, the controller 19 is configured to modulate the gasflow 13 with noise to produce gas flow oscillations 52/55 to vibrate theairways at different frequencies. Instead of using a patient specificfrequency, such as a resonant frequency, a random signal of randomfrequencies (noise) could be used by the controller to produce a noisyoscillating gas flow to encompass the majority of the population'soptimal resonant frequencies.

2.3.4 Resonant Frequency Chest

In another example, the controller 19 can control the system 10 so thatgas flow oscillations 51/54 are synchronised/matched or otherwisecorrespond with the resonant frequency of the chest wall of the patient.Respiratory inductance plethysmography (RIP) is a method of evaluatingpulmonary ventilation by measuring the movement of the chest andabdominal wall. The controller 11 can receive input from a chest band orother device/sensor 18 d to measure the chest wall movement. Thecontroller 19 then controls the flow source 12 to deliver an oscillatinggas flow 52/55 at a frequency that causes the most movement in the chestand abdominal wall to encourage gas movement and mixing, promotingoxygenation and/or CO2 clearance. The controller 19 might sweep the flowsource 12 oscillations through a range of frequencies to ascertain the(resonant) frequency that optimises chest and abdominal wall movement.

2.3.5 Diaphragm Contraction

In another embodiment, the controller 19 can control the system 10 sothat gas flow oscillations 52/55 are synchronised/matched or otherwisecorrespond with the frequency of the diaphragm muscle contraction.Electromyography (EMG) is a technique that evaluates and records theelectrical activity of muscles. The controller can receive input from anEMG system, which is used by the controller 19 to determine thefrequency of oscillation. The controller 19 then operates the flowsource 12 to provide a gas flow that oscillates 52/55 at the samefrequency as diaphragm muscle contraction to increase the mixing of thegases; promoting oxygenation and CO2 clearance.

2.3.6 Brain Activity

In another embodiment, the controller 19 can control the system 10 sothat gas flow oscillations 52/55 are synchronised/matched or otherwisecorrespond with the frequency of brain electrical activity. Thecontroller 19 can receive input from an EEG system or other sensor 18 d,which is used by the controller 19 to determine the frequency ofoscillation of neuron firing. The controller 19 then operates the flowsource 12 to provide a gas flow that oscillates 52/55 at the samefrequency as neuron firing which may increase the mixing of the gases,promoting oxygenation and CO2 clearance.

2.3.7 Additional Considerations

Sensing CO2 in the patient and providing that to the controller enablesfurther automatic adjustment of the gas flow components to optimise thecondition of the patient.

Sensing the oxygen saturation level and providing that to the controllerenables automatic adjustment of the gas flow components to optimise thecondition of the patient. The flow rate can be increased or decreased asoxygen saturation respectively decreases or increases

In another example, sensing the partial pressure of oxygen in the bloodis used to control the apparatus. The partial pressure of oxygen in theblood provides an indication of the amount of oxygen stored in the body.If this starts to fall—for example due to progressive atelactesis, thenmeasures should be taken to increase it. It is therefore advantageous tomonitor the partial pressure of oxygen in the blood with time, todetermine if it is falling (saturation measurements alone will not allowthis to be done accurately at high partial pressure levels). If thepartial pressure of oxygen in the blood starts to fall, the machine, orclinician, can take action to prevent further fall before the bloodoxygen saturation level starts to fall and the patient is compromised.

At the same time, the controller changes the characteristics of thewaveform so that the time for which the lower flow rate is appliedduring the cycle is decreased, and consequently, the time for which thehigher flow rate is applied is increased. In the case of oscillatingflow rates, when the flow rate oscillates towards the minimum flow rate,the time it remains at or near the minimum may be reduced compared withthe time it remains at or near the maximum flow rate. This can beachieved through summation of various oscillating components, throughcontrolling a duty cycle ratio of the waveform, providing a square wavecomponent with an appropriate ratio, or via other suitable means. Thisincreases the mean flow rate. The airway and lungs are held at higherpressure while the flow rate is at or near the maximum flow rate,therefore applying this characteristic to the waveform increases thetime for which the airway and lungs are held at a higherpressure—thereby increasing the mean pressure, and further reinflatingthe lungs. This is an example of the controller changing the waveformapplied.

The controller continues to monitor the blood oxygen partial pressurelevel. If the levels falls further, the controller increases the upper(maximum) and lower (minimum) flow rates again and also changes thefractions of the cycle for which the upper and lower flow rates areapplied as described above to further increase the airway mean pressure.

The gas flow can have an oxygen fraction of 100%, or 30-40% or 40-50% or60-70% or 80-90% or 90-100%. The gas flow can have an oxygen fraction ofat least about 21% and comprises one or more of nitrous oxide, nitricoxide and/or helium.

At any time during the monitoring and control process described above,the clinician may interrupt the monitoring and control cycle, andmanually set the value of upper (maximum) and lower flow (minimum)rates, and the period (frequency) of the flow variation cycle to valueswhich in their judgement may provide better outcomes for the patient.Following manual setting of these parameter, the clinician then has theoption of re-engaging the automatic monitoring and control process, orretaining the manually set values.

The gas flow can have a flow rate, wherein a first flow rate providedprior to the medical procedure and a second flow rate is provided duringthe medical procedure, and optionally a third flow rate after themedical procedure. The second flow rate can be greater than the firstflow rate; and/or the third flow rate is less than the second flow rate.The first flow rate is about 15 L/min to about 90 L/min, or about 20L/min to about 80 L/min, or about 25 L/min to about 60 L/min, or about30 L/min to about 50 L/min, or about 40 L/min, or about 30 L/min; and/orsecond flow rate is about 20 L/min to about 150 L/min, or about 40 L/minto about 120 L/min, or about 50 L/min to about 100 L/min, or about 60L/min to about 80 L/min, or about 70 L/min, or about 60 L/min; and/orthe third flow rate is less than about 90 L/min, or less than about 70L/min, or less than about 50 L/min, or less than about 40 L/min, or lessthan about 20 L/min, or about 40 L/min, or about 30 L/min.

In another example, exhaled CO2 is used as input for control of theapparatus. Exhaled CO2 information can be used as follows.

1. If the patient is breathing, the partial pressure of CO2 in the mouthwill rise substantially on the expiratory part of the breathing cycle.This is detected by the controller which is then able to automaticallydetermine if apnoea has commenced, and adjust the flow parametersaccordingly. This might—for example—consist of switching the flow froman initial constant flow rate of 30 l/min to a flow pattern which variescyclically in synchronism with the heart activity from a lower flow rateof 30 l/min to an upper flow rate of 70 l/min and then back again.

2.4 Examples of Using Varying Gas Flow for CO2 Removal and/orOxygenation

One exemplary and non-limiting example of an apparatus and method forsupplying a high flow of humidified gas for oxygenation and/or CO2removal, will be described with reference to FIG. 6 where the flow rateis cycled periodically to vary the pressure applied to the trachea andcause ventilation of the lungs. The apparatus is one example of thegeneric embodiment in FIG. 1. In this embodiment, the modulating deviceis a valve 60 after the humidifier.

In this setup dry gas, which may be air, oxygen, or any mixture of gasesappropriate for the therapy to be applied to the patient is suppliedfrom a flow source 12 to a humidifier 17 via a valve 59 which enablescontrol of the mean flow rate. A pressure regulator can also beincorporated into the gas supply. Mean flow rate and oscillating flowrate could be provided on two separately controlled lines, in analternative.

The humidifier 17 humidifies the gas to a level appropriate for thetherapy to be used—normally this would be to just below saturation levelat 37 degrees C., but may be any level appropriate for the patient. Thehumidified gas 13 passes through a two way proportional valve 60, whichis controlled by a controller 19. The proportional valve may divert gasto the patient, or to an exhaust—or to any combination thereof. Thepurpose of using a two way valve is to assist that flow through thehumidifier is as constant as possible (thereby providing optimumhumidification), notwithstanding that flow to the patient may vary overa wide range under the control of the controller.

The controller 19 controls the valve 60 to vary the flow rate going tothe patient cyclically to achieve a varying gas flow with the desiredoscillation parameters as previously described, leading to the desiredventilation described above. The controller 19 is provided with inputsignals from measurements of patient physiological functions forexample:—heart activity, spontaneous breathing etc. and physiologicalparameters for example:—levels of oxygenation, the partial pressure ofCO2 in the blood etc. It is able to synchronise the flow fluctuationswith periodic physiological functions so that the fluctuating flowcan—for example—operate to enhance the effect of cardiogenesis forapnoeic patients or enhance spontaneous ventilation for breathingpatients, where this is considered appropriate by the clinicians. Note,however, that in many applications—particularly for apnoeicpatients—breath synchronisation will not be necessary.

Parameters such as upper and lower flow rates, the period of the flowrate cycle, and the waveform of flow versus time during the flow ratecycle may be set by the controller from inputs provided either by ahuman operator, or automatically from measurements of patientphysiological functions and patient physiological parameters.

FIG. 7 shows the relationship between the delivered/applied flow rate,pharyngeal pressure, lung volume, and net flow of gas into and out ofthe lungs after dead space has been accounted for—for an apnoeic patientwith open mouth and typical airway dimensions.

In this example, the period of the flow rate cycle was 1 second and flowrate cycles were started at t=0. If a normal patient were ventilated inthis way, the minute volume achieved would be approximately 13 l—wellabove the minimum necessary.

FIG. 8 shows another example embodiment (this time a simplifiedarrangement) for use where the humidifier and circuit is able to respondto rapid fluctuations in flow. Here, the valve used to control the flowis a proportional valve which turns the overall flow in the system upand down.

Finally, FIG. 9 shows another example embodiment where the flow controlvalve is placed in the gas supply to the humidifier. This has advantagesbecause the proportional valve is able to work in dry gas—rather gaswhich is close to saturation point in humidity—and design of reliablemechanisms which provide rapid and precise control is easier if the gasis dry.

In these example embodiments, an optional pressure relief valve can beprovided close to the cannula in order to prevent barotrauma to thepatient in the event that the cannula seals into the nose and the mouthis closed. The pressure relief valve could be replaced by a pressuremeasurement system which is connected to the proportional valvecontroller, so that the controlled turns the flow off if the pressure atthe patient rises above a certain level.

As noted earlier, the present inventors have determined that byoscillating the flow (as described herein) in the trachea in a patientwho is not breathing spontaneously gas is driven down the trachea to thelungs, and then back up from the lungs to the trachea—that is, itprovides a mechanism for transporting gas in and out of the lungs.

2.5 Experimental Results Demonstrating Benefits of Varying Gas Flow

The following experimental discussion demonstrates this.

2.5.1 Experimental Apparatus

A benchtop experimental model was used to investigate the effects ofoscillating high nasal flow (HNF) on gas exchange and carbon dioxide(CO2) clearance during apnoea. The model is a suitable representation ofthe embodiments of the apparatus 10 described herein and is shown inFIGS. 12A, 12B.

The model consisted of an adult upper airway geometry connected to alung reservoir with compliance similar to that of the lung-chest wallsystem in real physiology (approximately 45 ml/cmH2O). It included thenasal and pharyngeal cavity, an open mouth, trachea, and primary andsecondary bifurcations up to the sixth generation. The lung reservoirwas plumbed with various controllers and sensors to introduce/monitorpercent concentration of CO2 in the lung, measure the incoming flows,and monitor the static lung pressure.

In addition, a cardiogenic pump was used to simulate the effects of theheart on gas motion in the airways. It is thought that the pulsatilenature of blood flow (caused by effects of the heart) causes minisculesqueezing of the lower airways which in turn drives a plug of gas in theupper airways and trachea. The pump consisted of a numericallycontrolled stepper motor-syringe system and oscillated a known volume ofgas at a specific wave shape and frequency into the lung reservoir.Cardiogenic oscillations can be approximated with a trapezoidal waveformof with amplitudes (stroke volume) of 5-30 mL and frequency of 0.5-3 Hz.The cardiogenic parameters (waveform, frequency, and stroke volume) willvary between patients and within the same patient at different times dueto the variability in heart rate and blood pressure. FIG. 11 shows anexample of a piece-wise linearly approximated cardiogenic waveform withparameters derived from one experimental realisation. The fit was basedon a heart rate of 64.2 bpm, stroke volume of 22.5 mL, and rise anddelay fractions of 0.7 and 0.15 respectively. FIG. 11 also includesplots of shifted sinusoidal waves which illustrate (but not to scale)the phase shifting in the varying high gas flow and that will bediscussed in example 3 (note that positive values imply gas pushing intothe lungs).

Referring to the experimental apparatus 120 in FIG. 12A (which is asuitable model for the apparatus 10 of embodiments described herein),gas flow oscillations were delivered using a flow source 121 from a wallsupply 122A, bottle supply 122B and/or blower 122C) to the nasal cavityusing a high flow nasal cannula which was connected in series to aregulator and a proportional valve. The latter is an electronicallycontrolled orifice-type valve with sufficient resolution to producearbitrary waveforms composed of multiple frequencies. In clinicalpractise one or more valves could be positioned near the gas source(wall, bottle, or blower) with or without a regulator/pressure relief inseries; prior or post the humidifier 124 and/or the control system; andprior or post the end of the delivery circuit but before the cannula 123(see FIG. 12A). There are certain advantages of placing the valve insuch locations. For example, valves near the gas source or inlet couldshut-off or divert the flow in case of medical emergencies or whenexcess pressures are sensed at the patient end. Placing the valves nearthe humidifier/controller simplifies device integration with the rest ofthe system. Placing the valve in close proximity to the cannulaminimises the dissipations of high frequency flow oscillations in thepatient's circuit due to the compliant nature of respiratory conduits.

The method for flow oscillations is not limited to electronicproportional valves as other devices such as diaphragms, flow choppers;mechanical flutters or pressure relief valves can also be used. Forexample, FIG. 12B illustrates the use of an underwater pressure reliefsystem to generate broad spectrum of oscillations that are dictated bythe number, calibre, orientation, and depth of the immersed tube. Theflow rate, cross section of the tube orifice and the surface tension ofthe liquid could also impact the nature of oscillations. Thisoscillation mechanism differs from the bubble CPAP as the flowfluctuations occur upstream of the patient end.

The experimental procedure consisted of applying a fixed concentrationof CO2 into the lungs (at about 9.5-10%), allowing the system tostabilise, then applying the high gas flow therapy (nasal high flowtherapy—NHF) and monitoring the decay of CO2 with time from the lungsreservoir. A sample of the results is shown in FIG. 13 and includes theCO2 infusion, stabilisation period and the decay of CO2 concentration inthe lung after commencement of therapy. The gradient of the dotted linesignifies the decay rate.

Aside from its clinical relevance, the CO2 decay rate was used in theexamples below because it is a direct measure of gas exchange betweenthe lungs and the outside environment. In these experiments, dry air wasused as the incoming high flow gas mixture but it should be noted thatother gases or gaseous mixtures (such as pure oxygen saturated withwater vapour at 37 degrees, mixtures of O2, N2, and helium) are alsopossible. The initial clearance rate was calculated as the gradient ofthe concentration-time curve for the first five minutes of therapy andmultiplied by the lung volume to obtain gas exchange data in millilitresper minute. The data in the following examples have been normalised tothat without oscillations to calculate the enhancement factor.

In one example, a vibrating mesh nebuliser was connected to the upperairway model, about 5 cm above the carina and produced a mist of water(mean particle size<4 um) to allow for flow visualisation. The gasmotion was simultaneously captured with a high speed camera at 900 fpsand later analysed using image processing software (ImageJ, and Matlab)to estimate time of flight and bulk gas velocity.

The following examples illustrate how varying the flow rate promotes gasexchange in the lungs, the presence of a useful frequency range whereCO2 clearance is enhanced, the advantages of syncing the NHF waveformwith the heart signal, the advantages of combining multiple frequencies,and the advantages of varying the wave shape. Note, the examples shouldnot be considered exhaustive of the nature of the oscillating gas flowsthat will be effective and clearing CO2. Rather, they demonstratenon-limiting particular examples of the benefits of oscillating gasflows. Gas flow oscillations with parameters and parameter values (e.g.frequency, phase, amplitude and the like) other than those tested willalso be effective at clearing CO2.

2.5.2 Example #1

It has been previously suggested that one of the benefits of NHF, inaddition to flushing parts of physiologic dead space (nasal cavity downto larynx region), is the modest increase of static lung pressure. Thispressure typically scales as the approximate square of flow rate, and ison the order of 1 cmH2O (compared with ˜15 cmH2O during mechanicalventilation). Pressures generated with NHF are thought to be beneficialin preventing lung atelectasis in apnoea which, in turn, improves theventilation/perfusion matching of the respiratory system and preventsdesaturation. It was surprising to find that the pressure changesgenerated as a result of oscillating the flow in an open HNF system weresufficient enough to promote gas movement in the upper airways and intothe lungs. Examples of lung pressures as a function of constant andvarying NHF rates are shown in FIGS. 14 and 15A. The FIG. 14 highlightsthe square nature of the pressure-flow relation and suggest thatoscillating high flow is more effective than oscillating low flows (foradults, those are typically at or below 15 L/min). The high flow ratesused clinically on adults could reach up to 150 L/min, or more, forexample. FIG. 15A demonstrates that sinusoidal flow oscillations between35-105 L/min at a frequency of 1 Hz can effectively promote pressurechanges (with phase lag dependent on airway resistance) which in turncan improve volumetric flow into/out of the lungs as consequence of lungcompliance (the pressure/volume relation).

FIG. 15B shows a sequence of high speed images captures at about 6 msintervals and demonstrate the motion of gas during the initial part of asinusoidal flow oscillation between 30-100 L/min at 1 Hz. This bulkconvection is fast (about 1 m/s) and is responsible for exchanging CO2from the lower airways of the lungs with the fresh incoming gas abovethe larynx during each oscillation. The distance a parcel of gas travelsduring a single flow oscillation is not only dependant on the flow ratebut also on the frequency of oscillation and the shape of the waveformas those will dictate gas acceleration, time of flight and any intra- orinter-parcel mixing that may take place. The latter is thought to bebeneficial in improving gas exchange as the concentration gradientsalong the lung airways are reduced.

2.5.3 Example #2

Nasal high flow was delivered with nasal cannula (large) and oscillatedbetween 30 and 100 L/min at frequencies between 0-20 Hz using asinusoidal waveform. Cardiogenic oscillations were applied at afrequency of 1 Hz at 270 degrees out of phase to the flow with a strokevolume 22.5 mL.

Furthermore, matching the phase (i.e. synchronising) of nasal high flowand cardiogenic oscillations can provide an additional improvement inCO2 clearance by nearly a factor of 6. This suggests that it would bebeneficial to have at least one waveform with a period matching that ofthe heart activity and with constant relative phase to that signal.Resting heart rates are typically between 40-100 bpm (0.67-1.67 Hz) butcould be in the range of 30-180 bpm (0.5-3 Hz) under extreme physiology(e.g. under medical procedures or intense exercise).

It is worth noting that matching the NHF phase shift to that ofcardiogenic oscillations is most meaningful when the two frequencies areidentical, otherwise phase shift is inevitable.

2.5.4 Example #3

Nasal high flow was delivered with nasal cannula (large) and oscillatedbetween 6 L/min (amplitude minimum) and 136 L/min (amplitude maximum) at1 Hz and 10 Hz simultaneously (FIG. 9—top panel). The cardiogenicoscillations were applied at a frequency of 1 Hz and phase shiftedbetween 0 and 270 degrees in 90 degree increments to the nasal high flow(see FIG. 16—bottom panel). The stroke volume was set to 22.5 mL with afrequency of 1 Hz.

The clearance rates indicate that syncing with the heart (a phase shiftof 0) provides twice the enhancement to the contrary (a phase shift of180 degrees) (see FIG. 17). This is because the combined effects of flowand cardiogenic volume changes in the trachea are physically added;thus, amplifying gas motion. That said, good clearance is still achievedat other phase shifts, such as or about 90 degrees, 180 degrees, 270degrees or any other phase shift. The enhancement at any phase shift isstill great than the base flow, which demonstrates that frequencymatching is beneficial at any phase off-set. It is worth noting that theexact value of the phase shift is highly dependent on the shape and insome cases amplitude of the cardiogenic waveform as the addition ofsinusoid and non-idealised trapezoid could be non-intuitive. Inaddition, the plug of gas displaced in the trachea with each cardiogenicoscillation may not take place instantaneously after every heart beatdue to delays in the transmission of the pulsatile wave from the blood,through the airway tissues and into the gas where acceleration of thegas parcels would then take place. These delays in transmission woulddepend on the patient's physiology (e.g. heart rate, blood pressure,airway resistance etc.) and it is therefore more useful to sync with thecardiogenic pulse in the gas phase. This can be done by matching thefrequency with the heart activity and either measuring, or inferring thephase shift (by calculation or CO2 clearance measurements).

Note that in a clinical setting the patient's physiology may vary withtime and therefore the phase shift should also be a variable. This meansthat syncing with the heart signal could be in-phase (or with constantrelative phase), out of phase or anything in between. In the cases wherethe variability is too large it might be beneficial to use a measured orcalculated mean phase shift value where the NHF and heart signals arematched in a time-averaged or population-averaged sense.

3. Embodiment of Apparatus/Method for Assisting with Oxygenation

3.1 Oxygenation During Medical Procedure

Using the apparatus described above, another embodiment is provided forachieving oxygenation, during anaesthesia or other medical procedure

Referring to the flow diagram in FIG. 2, the method using the system ofFIG. 1 will be described. The controller is configured to carry out thedetermination of oxygen requirements and to control the parameters ofhigh gas flow for oxygenation and/or CO2 removal. First, during apre-anaesthesia stage, the controller determines oxygenationrequirements of the patient, step 21. These can be oxygenationrequirements that are based on the prediction of what might be requiredbefore and/or during anaesthesia based on historical/empirical data. Thecontroller 19 receives input from the sensors 18 a-18 d and/or the uservia the input interface 20. From that input and/or stored data (such aslook up tables, historical data, parameters, relationships, the graphsor the like) the controller determines the oxygenation requirement, step21. The determination could take place through any processing, look uptable, relationship (empirical or mathematical) or the like.Non-exhaustive examples of such input and determination processing areas follows. One or more alone or in combination could be used to makethe oxygen requirement determination.

The user (such as anaesthetist or other clinician, or the patient)provides, input via the interface 20, a pre-operative assessment toestimate the level of risk for every patient. This level of risk relatesto the risk of the patient entering hypoxia during anaesthesia. Thecontroller then determines oxygenation requirements, step 21, based onthe level of risk and/or the user (e.g. anaesthetist or clinician)provides input indicative of the actual oxygenation requirement and/ordose/therapy settings and/or the actual parameter settings for the highflow gas delivery. Any of the input could be provided as a setting orrange of settings or as one or more input values. The system could alertthe user of the recommended settings or control the system to providethe settings, as to be described later.

Alternatively or additionally, and more generally, the user entersinformation from which oxygenation requirements can be determined, suchinformation not necessarily directly indicating risk levels, or notbeing indicative of risk levels at all.

Sensor input could be used alternatively or additionally.

Next, once oxygenation requirements are determined, the controller 19operates the flow source 12, humidifier 17 and/or other aspects of thesystem 10 to control the parameters of the high flow gas 13 delivered tothe patient, step 22, so that the gas flow 13 meets the oxygenationrequirements during a pre-anaesthesia (pre-oxygenation) stage. This cancomprise altering one or more of:

flow rate of gas (such as flow rate of oxygen)

volume of gas delivered

pressure of gas

composition and/or concentration of gas

Examples of user input for determining oxygenation requirements and theresultant parameter settings are as follows.

-   -   The user enters the value on a scale. For example the user could        choose a number from 1 (minimal risk) to 10 (high risk). The        system could then choose the optimal settings for that scale        number.    -   The user enters information such as age, weight, BMI, lung        volumes, metabolic rate, body fat measure (e.g. percentage)        and/or other patient factors that could be used individually or        any combination to choose the optimal therapy settings (oxygen        requirements). For example, a sum score method could be used        with two or more of the factors listed. This can be used to        predict the level of support (oxygenation) that will be required    -   The user enters pre-existing patient conditions. For example, if        a patient is at risk of barotrauma the flow could be minimised        to meet peak inspiratory demand but not deliver excess flow.    -   Existing limits on hardware could be used to choose the optimal        therapy settings. For example, if the surgical environment is        experiencing a shortage in oxygen the settings could be altered.        100% oxygen could be delivered only during inspiration and the        flow could be set to meet the patient's peak inspiratory demand        to ensure minimal wastage

Different levels of support could be optimal in different stages ofundergoing anaesthesia. The high flow system 10 can optionally detectwhen a change in stage has occurred and alert the user or automaticallydetermine new oxygenation requirements and/or change the gas flowparameters to me those new requirements. For example, after thepre-oxygenation stage, the patient is administered the anaesthesia andenters and anaesthesia stage. Breathing function can diminish and thepatient can become apnoeic. Different oxygenation requirements exist tothose pre-anaesthesia.

Therefore, the controller 19 is further configured to detect theanaesthesia stage (or change in anaesthesia stage), step 23. Possiblemethods for detecting a change in state are as follows.

-   -   The controller uses the pressure waveform (from a pressure        sensor) to detect when the patient is breathing or not (e.g.        transition from pre-oxygenation to apnoea).    -   The controller uses the expired CO2 waveform (from a sensor) to        detect when the patient is breathing or not (e.g. transition        from pre-oxygenation to apnoea)

While the controller 19 is monitoring the state, step 32, the high flowgas 13 is delivered as per the parameters previously determined and set.After a change in stage is determined (such as transitioning from thepre-oxygenation stage to the anaesthesia stage) the controller/system19/10 can continue delivering gas flow 13 with the same parametersettings. However, the system 10 can also go into a monitoring phase,step 24, wherein by the oxygenation requirements are re-determined,optionally in a continuously or periodic manner, step 24. Again previousor fresh input from a user via the input interface 20 can be used todetermine the oxygenation requirements, in addition or alternatively tousing sensor input 18 a-18 d. The oxygenation requirement can bedetermined in the same manner as described above for the pre-oxygenationstage, with the possible difference being that it is re-determinedcontinuously or periodically based on updated input from the sensorsand/or user.

The gas flow 13 parameters are then adjusted by the controller 19 tomeet new oxygen requirements, these parameters being the same asdescribed above, step 25. Even if updated input is not received, theoxygenation requirement might be re-determined on the basis that thestage of anaesthesia had changed, or alternatively the oxygenationrequirement is not specifically re-determined, but a differentoxygenation requirement is presumed and the high flow gas parameters areset accordingly for the new stage.

3.2 Oxygenation Using Flow

A particular non-limiting example of the function due to change inanaesthesia state as shown in FIG. 3. After the system started, step 30,the system monitors the patient and detects breathing, step 31, anddetermines a pre-oxygenation stage. The system provides gas flowparameters, including a flow rate of 40 L per minute, which are suitablefor the pre-oxygenation stage, based on typical oxygenationrequirements. After further monitoring of the patient, the systemdetects an apnoea, and assumes that the anaesthesia stage has started,step 32. That changes the parameters of the gas flow to a flow rate of70 L per minute which meets the oxygenation requirements of the apnoeicstage, step 32.

A continuous supply of oxygen and removal of carbon dioxide is importantto sustain healthy respiratory function. In addition to the methoddescribed above relating to determining and providing oxygenationrequirements, the system can also be configured to monitor supply ofoxygen and removal of carbon dioxide, step 24 as in FIG. 2. Possiblenon-limiting methods of monitoring these comprise:

-   -   monitoring expired O2 and CO2 (using e.g. sensors)    -   monitoring transcutaneous O2 and CO2    -   monitoring blood gases (e.g. pulse oximeter)    -   monitoring SpO2    -   monitoring partial pressure of O2 and/or CO2    -   monitoring RIP        -   any other suitable physiological parameters described            herein.

In step 24, the trends/values of these parameters described above couldbe used to detect when the therapy settings (gas flow parameters) couldbe changed. The system is configured to then alert the user orautomatically control the therapy dose (that is, gas parameters).

For example, if the SpO2 starts to decrease past 90%, the flow and oroxygen concentration (if not already at 100%) could increase to providea higher level of support, step 25. If the end-tidal CO2 value or trendshows an increase, the therapy support could increase as a higher levelof support is needed, step 25. This should not be limited to oxygen andcarbon dioxide. Other measured parameters (e.g. heart rate, bloodpressure) could also be used to change the therapy dose settings.

In further embodiments, when the predicted or monitored pre-oxygenationor apnoeic time is small, the gas parameters can be changed accordingly.For example, if the estimated time of the anaesthesia stages(pre-oxygenation or during anaesthesia/apnea) is too short, the gasparameters can be adjusted to provide a higher level of support for moretime—for example the oxygen concentration, flow rate, oxygen volume,pressure and/or gas composition can be changed, for example.

As relatively high gas delivery flow rates may be used with theembodiments or configurations described herein, the gases being suppliedor delivered to the user or patient can may be delivered to differentparts of the user's or a patient's airway.

For example, according to those various embodiments and configurationsdescribed herein, a flow rate of gases supplied or provided to aninterface or via a system, such as through a flow path, may comprise,but is not limited to, flows of 15 litres/min to 150 litres/min andoptionally at least about 40, 50, 60, 70, or 80 L/min, or more, anduseful ranges may be selected between any of these values (for example,about 40 to about 80, about 50 to about 80, about 60 to about 80, about70 to about 80 L/min, or any other subrange of 15 litres/min to 120Litres/min).

Such relatively high flow rates of gases may assist in providing thesupplied gases into a user's airway, or to different parts of a user'sairway, for example such flow rates may allow for a delivery of suchgases to the upper or lower airway regions as shown in FIG. 4. Upperairway region typically includes the nasal cavity, pharynx and larynx,while the lower airway region typically includes the trachea, primarybronchi and lungs.

The embodiments described can utilise the knowledge of the respiratoryflow wave and/or the transition between inspiration and expiration. Forexample methods and apparatus for respiratory flow wave, meeting (e.g.peak) inspiratory demand and estimating (e.g. peak) inspiratory demandcould be used. It should also be noted that the following can utiliseswitching modes of operation between inspiration and expiration. Theexact moment of switching should not be limited to the exact transitionpoint.

As described above, gas flow parameters are changed to provide therequired oxygenation and/or removal of CO2. This can be by way ofadjusting e.g. gas flow rate and/or pressure.

The foregoing description of the invention includes preferred formsthereof. Modifications may be made thereto without departing from thescope of the invention.

The invention claimed is:
 1. An apparatus for oxygenation or CO₂clearance of a patient, or a combination thereof, during a medicalprocedure wherein during the medical procedure the patient is apnoeicfor at least a portion of the medical procedure or the patient is underanesthesia causing diminished or risk of diminished respiratoryfunction, comprising: a flow source or a connection for a flow sourceconfigured to provide a gas flow; a gas flow modulator; and a controllerconfigured to control a flow rate of the gas flow during apreoxygenation stage of the medical procedure or when the patient isunder anesthesia, the controller configured to control the flow rate bycontrolling the gas flow modulator to oscillate the flow rate based onan oscillating flow rate component and a base flow rate component toprovide a varying gas flow with one or more frequencies, wherein thecontroller is configured to control the gas flow between a set flow ratebefore the patient is apneic, or has a diminished, or is at risk ofdiminished, respiratory function and a base flow rate of the base flowrate component when the patient is apneic, or has a diminished, or is atrisk of diminished, respiratory function; and wherein the apparatus isconfigured to provide the gas flow to a non-sealing patient interface.2. The apparatus according to claim 1 wherein the oscillating flow ratecomponent has an oscillating flow rate and the controller is configuredto control the gas flow modulator to provide the oscillating flow ratewithin a range of about 0 litres/min to about 375 litres/min.
 3. Theapparatus according to claim 2 wherein the base flow rate of the baseflow rate component is within a range of about 0 litres/min to about 375litres/min.
 4. The apparatus according to claim 2 wherein the base flowrate of the base flow rate component is in a range of about 0.2litres/min per patient kilogram to about 2.5 litres/min per patientkilogram.
 5. The apparatus according to claim 2 wherein the flow sourceor the connection for the flow source is configured to provide the gasflow for use on persons greater than about 30 kg.
 6. The apparatusaccording to claim 2 wherein the oscillating flow rate comprises one ormore frequencies in a range of about 0.1 Hz to about 3 Hz.
 7. Theapparatus according to claim 2 wherein the oscillating flow rate is in arange of 0.05 litres/min per patient kilogram to 2 litres/min perpatient kilogram.
 8. The apparatus according to claim 2 wherein the flowsource or the connection for the flow source is configured to providethe gas flow for use on persons within a range of about 0.3 to 30 kg. 9.The apparatus according to claim 2 wherein a base flow rate of the baseflow rate component is about 8 litres/min for a person under about 2kilograms.
 10. The apparatus according to claim 1 wherein the gas flowmodulator comprises an underwater pressure release valve, anoscillatable diaphragm, an in-line linear actuator, a flow chopper, anaerodynamic flutter valve, a mechanical flutter valve, or a proportionalvalve.
 11. The apparatus according to claim 1 wherein the gas flowmodulator is in or after the flow source.
 12. The apparatus according toclaim 1 wherein the gas flow has an oxygen fraction of 100%, or in arange of 30-40% or in a range of 40-50% or in a range of 60-70% or in arange of 80-90% or in a range of 90-100%.
 13. The apparatus according toclaim 1 wherein the gas flow is air.
 14. The apparatus according toclaim 1 wherein the non-sealing patient interface comprises or isconfigured for use with a high flow nasal cannula.
 15. The apparatusaccording claim 1 further comprising a humidifier to humidify the gasflow before or after it is oscillated.
 16. The apparatus according toclaim 1 wherein the controller is configured to determine when theapnoea in the patient has commenced or to detect an anaesthesia stage orchange in anaesthesia stage in the patient.
 17. The apparatus accordingto claim 10 wherein the gas flow modulator is or comprises theproportional valve, and the proportional valve has a variable sizeorifice that is variable based on an electrical signal.
 18. Theapparatus according to claim 3 wherein the base flow rate is within arange of about 30 litres/min to about 90 litres/min.
 19. The apparatusaccording to claim 1 wherein the one or more frequencies comprises atleast two frequencies.
 20. The apparatus according to claim 19 whereinthe at least two frequencies are in a range of about 0.1 Hz to about 3Hz.
 21. The apparatus according to claim 1 wherein the base flow rate ishigher than the set flow rate.
 22. A method for oxygenation or CO₂clearance of a patient, or a combination thereof, comprising:controlling, via a controller, a gas flow to the patient via anon-sealing nasal interface during a preoxygenation stage of a medicalprocedure or when the patient is under anesthesia; determining ordetecting a stage of the medical procedure; and based on the stagedetermined or detected, varying the gas flow delivered to the patient byoscillating a flow rate of the gas flow based on an oscillating flowrate component and a base flow rate component when the patient is apneicor has a diminished risk or is at risk of diminished respiratoryfunction; wherein the varying gas flow comprises a set flow rate beforethe patient is apneic, or has a diminished, or is a risk of diminished,respiratory function and a base flow rate of the base flow ratecomponent when the patient is apneic, or has a diminished, or is at riskof diminished, respiratory function.
 23. The method according to claim22 wherein a base flow rate of the base flow rate component is in arange of about 0.2 litres/min per patient kilogram to about 2.5litres/min per patient kilogram.
 24. The method according to claim 22wherein the non-sealing nasal interface comprises or is configured foruse with a high flow nasal cannula.
 25. The method according to claim 22wherein the determining or detecting the stage of the medical procedurefurther comprises determining when the apnoea in the patient hascommenced or detecting an anaesthesia stage or change in anaesthesiastage in the patient.
 26. The method according to claim 22 wherein thevarying gas flow comprises at least two frequencies.
 27. The methodaccording to claim 26 wherein the at least two frequencies are in arange of about 0.1 Hz to about 3 Hz.
 28. The method according to claim22 wherein the base flow rate is higher than the set flow rate.